Tag Archives: sun

Sun’s coronal loops could be optical illusions

An active region of the sun just rotating into the view of NASA’s Solar Dynamics Observatory gives a profile view of coronal loops over about a two-day period, from Feb. 8-10, 2014. (Image credit: NASA/Solar Dynamics Observatory)

Everyone knows the picture of the sun. A bright orange ball with jets of fire spewing out thousands of miles into space with temps soaring above a million degrees. However, a new study from the National Center for Atmospheric Research (NCAR) brings into question coronal loops existence at all.

The report, published in The Astrophysical Journal, found that these may actually be optical illusions. While the researchers were able to pinpoint some of the coronal loops they were looking for, they also discovered that in many cases what appear to be loops in images taken of the Sun may in fact be wrinkles of bright plasma in the solar atmosphere. As sheets of bright plasma fold over themselves, the wrinkles look like bright thin lines, mimicking the look of distinct and self-contained strands of plasma.  

“I have spent my entire career studying coronal loops,” said NCAR scientist Anna Malanushenko, who led the study. “I was excited that this simulation would give me the opportunity to study them in more detail. I never expected this. When I saw the results, my mind exploded. This is an entirely new paradigm of understanding the Sun’s atmosphere.”

Coronal loops are found around sunspots and across active regions of the Sun. These structures are associated with the closed magnetic field lines that connect attractive regions on the solar surface. Many coronal loops last for days or weeks, but most shift quite rapidly. The assumption that they exist is a normal one for scientists because it suits the most basic understanding of magnetism.

The findings, which have been coined the “coronal veil” hypothesis, could have substantial implications for solar research. These coronal loops have been used for decades as a way to garner info about density, temperature, and other physical characteristics of the solar atmosphere.

“This study reminds us as scientists that we must always question our assumptions and that sometimes our intuition can work against us,” Malanushenko said.

The research relied on a realistic 3D simulation of the solar corona produced by MURaM, a radiative magnetohydrodynamic model that was extended to replicate the solar corona in an effort led by NCAR several years ago. The model allowed the researchers to slice the corona in distinct sections in an effort to isolate individual coronal loops.

Since there is a significant magnetic field in the Sun, the existence of magnetic field lines that could trap a rope of plasma between them and create loops seems like an obvious explanation. And in fact, the new study confirms that such loops still likely exist.

However, the loops seen on the Sun have never really behaved exactly as they should, based on the knowledge of magnets. As an example, scientists would assume the solar magnetic field lines to expand as they move higher in the corona. Therefore, the plasma trapped between the field lines should also spread out between the boundaries, creating thicker, dimmer loops. But images of the Sun do not show this. Instead, they show the opposite. The loops further out still appear thin and bright.

The possibility that these loops are instead wrinkles in a coronal veil help explain this and other inconsistencies with scientists’ expectations of coronal loops. It also brings into question new mysteries such as what determines the shape and thickness of the folds and how many of the apparent loops in images of the Sun are actually real strands, and how many are optical illusions.

For the first time, the research group was also able to capture the entire life span of a solar flare, from the build-up of energy below the solar surface to the emergence of the flare at the surface, and finally to the fiery release of energy.

Malanushenko said that understanding the number of coronal loops which are actually optical illusions will require continued observations that probe the corona and new data analysis techniques.

“We know that designing such techniques would be extremely challenging, but this study demonstrates that the way we currently interpret the observations of the Sun may not be adequate for us to truly understand the physics of our star.”

Scientists develop AI to identify holes in the Sun’s corona

If you’ve ever seen images of the Sun, you may have noticed some dark marks on the surface of the corona, the aura of plasma that surrounds the Sun and other stars. These dark spots are massive areas that are colder than the surrounding corona — still very hot, mind you, just not as hot as the rest of the corona. Now, astronomers have a new way of identifying them.

The AIA instrument of SDO captured this image of the sun showing an X1.1 class flare on Nov. 8, 2013 . Credits: NASA

Usually, astronomers observe and identify coronal holes using Extreme Ultraviolet (EUV) and X-ray light detectors. However, it is hard to differentiate the dark features which are holes from other dark spots, such as filaments. It’s easy to tell there’s a dark area on the solar corona, but figuring out what that dark spot is not as easy.

Now, a team of scientists developed an artificial neural network called CHRONNOS (Coronal Hole RecOgnition Neural Network Over multi-Spectral-data) to identify the coronal holes. They used data collected by SDO (Solar Dynamics Observatory) NASA satellite, from November 2010 to December 2016, to train and test the model.

The magic of the model lies in giving data with an increasing image resolution. Starting for example, with 8×8 pixels, then 64×64 pixels, and finally 512×512 pixels. This is done to give as much information to the AI and for faster performance, lower-resolution data is easier for the network to analyze. 

As you can see in the video, the team used the timelapse of the last two months of each year from 2010 to 2019. The red contours show the holes over the days with a surprisingly smooth transitional variation.

The new method was successful at detecting 261 coronal holes within that time period with 98.1% of correct detections. The team also compared the relation between the holes detected with sunspots. They have concluded that their model is independent from solar activity, whether it’s in its maximum or minimum. 

The study was published in Astronomy & Astrophysics.

How many Earths can you fit inside the sun?

From the vantage point of a human, our world truly is huge. However, in the grand, cosmic scheme of things, the Earth is but a drop in the solar bucket.

The sun is a star at the center of the solar system, a sphere made up of hot plasma and magnetic fields. Its diameter is about 1,392,000 km (864,000 miles), nearly 109 times larger than the Earth, and its mass is 330,000 times that of the Earth. In fact, by mass, the sun makes up over 99.86% of the solar system, whereas gas giants like Jupiter and Saturn comprise most of the remaining 0.14%.

In order to comprehend the sheer scale of the sun, it’s worth asking the question: how many Earth-sized planets can you fit inside the sun?

Volume-wise, you could fit nearly 1.3 million Earths into the sun (1.412 x 1018 km3). That’s assuming all those millions of Earths are squished together with no empty space in between. But the Earth’s shape is spherical not a cube, so only about 960,000 Earths would fit inside the volume of the sun.

Here’s how it would look like (approximately) if the Earth was a tiny blue marble:

The sun is just an average-sized star, though. For instance, the red giant Betelgeuse has a radius 936 times that of the sun, making it billions of times larger in volume than the Earth.

And that’s nothing. VY Canis Majoris is thought to have between 1,800 and 2,100 times the radius of the sun. Therefore, you could fit dozens of billions of Earths in some of the largest stars in the universe.

This illustration shows the approximate sizes of the planets relative to each other. Credit: Wikimedia Commons / NASA/ A. Simon.

Earth is neither the largest nor the smallest planet in the solar system. Mercury (0.055 times Earth’s volume), Venus (0.85 times Eath’s volume), and Mars (0.151 times Earth’s volume) are all smaller than Earth. It would take 17.45 million Mercury-sized planets, 1.12 million Venus-sized planets, and 6.3 million Mars-sized planets to fill the sun, gaps not included.

On the opposite end, you could fit 726 Jupiter-sized planets (1,321 times the volume of Earth) and 1,256 Saturn-sized planets (764 times the volume of Earth) inside a hollow sun, gaps not included.

In the future, you could cram even more Earths or Jupiters into the sun. As it drags closer to the end of its lifecycle, the sun gets both hotter and larger as it continues to fuse hydrogen into helium at its core. When it runs out of fuel, the core will collapse and heat up ferociously, causing the sun’s outer layers to expand.

By astronomers’ calculations, the sun is already 20% larger than at the time of its formation roughly five billion years ago. In another five billion years, when it will reach its helium-burning phase, the sun will turn into a red giant. It will be so large at this time that it will completely engulf the planets Mercury, Venus, and perhaps even Earth.

We’re inching closer to a better sunscreen that won’t kill corals (unlike our current options)

New research is paving the way towards new, more efficient sunscreen — one that won’t damage corals, to boot.

Methylene blue. Image credits amandabhslater / Flickr.

Methylene blue, a century-old medicine that my grandma used to give me whenever I had a sore throat, could prove to be quite an effective sunscreen. The substance is an effective broad-spectrum insulator against ultraviolet (UV) radiation, absorbing both UVA and UVB (the first produces sunburn, the second contributes to skin cancer), repairs UV-induced DNA damage in the skin, and is also much safer for corals than current options. According to a new study, methylene blue could become a common alternative sunscreen ingredient.

Sun? Blocked.

“Our work suggests that methylene blue is an effective UVB blocker with a number of highly desired characteristics as a promising ingredient to be included in sunscreens,” says the study’s senior author Dr. Kan Cao, Founder of Mblue Labs, Bluelene Skincare, and a Professor at the University of Maryland Department of Cell Biology and Molecular Genetics.

“It shows a broad spectrum absorption of both UVA and UVB rays, promotes DNA damage repair, combats reactive oxygen species (ROS) induced by UVA, and most importantly, poses no harm to coral reefs.”

Most commercially available brands of sunscreen sold today (around 80%) use oxybenzone to block UV rays. However, we know that oxybenzone is quite damaging to coral reefs, and several local and national governments have already banned its use and that of its derivatives in order to protect marine ecosystems. Which is all well and good, but it also means that we need a replacement.

The team looked at the interaction between methylene blue and UV radiation under several angles in primary human keratinocytes and skin fibroblasts from young and old donors. The results were compared to similar data for oxybenzone. They report that methylene blue not only absorbs UVA & UVB, but it also helps repair DNA damage induced by UV radiation.

When exposing Xenia umbellate, a soft coral species, to the same amounts of methylene blue or oxybenzone in isolated tanks, they found another important tidbit of information. The corals exposed to oxybenzone experienced severe bleaching and death in under a week. The ones exposed to methylene blue did not show any negative effects even at relatively high concentrations of the compound.

Compared with other skincare antioxidants such as vitamin A (retinol) and vitamin C, methylene blue showed that it is highly effective at protecting our cells. The best results, however, were seen when using a combination of vitamin C and methylene blue.

“We are extremely excited to see that skin fibroblasts, derived from both young and old individuals, have improved so much in terms of proliferation and cellular stress in a methylene blue-containing cell culture medium.” Dr. Cao reports.

“Most surprisingly, we found that the combination of methylene blue and Vitamin C could deliver amazing anti-aging effects, particularly in skin cells from older donors, suggesting a strong synergistic reaction between these two beneficial antioxidants.”

Overall, the team writes in their abstract, methylene blue has the potential of becoming a reef-friendly active ingredient in sunscreens, which would also likely improve the efficiency of this product compared to current options. In particular, they explain, today’s ratings (Sun Protection Factor — SPF) only account for UVB exposure, so today’s sunscreens leave users exposed to the oxidative stress and photoaging induced by UVA rays. Methylene blue also promotes DNA repair in the skin, and can deliver anti-aging effects, especially in conjunction with vitamin C.

The paper “Ultraviolet radiation protection potentials of Methylene Blue for human skin and coral reef health” has been published in the journal Scientific Reports.

How hot is the sun?

The Sun is a ball of nuclear plasma so large its own weight keeps it from exploding. Very cool, but also quite hot. However, the Sun has a complicated interior structure, and surprisingly large temperature variations, both on and under its surface. Today, we’re going to look at why this is, and how we know.

A ‘Pumpkin Sun’ composite image created by NASA in 2014. Colored gold-yellow, with active regions being brighter for “a particularly Halloween-like appearance”. Image credits NASA.

A lot of the things happening on Earth are, ultimately, fueled by energy from the Sun. We see that energy as sunshine, feel it hot on our skin on a clear day. It drives winds, and it powers rain cycles. Almost all life on Earth is fed by plants capturing sunlight. It’s very fortunate for us, then, that the Sun produces a monumental amount of energy. Just a fraction of its output reaches our planet, since a lot of it is lost in transit, reflected, or radiates away from Earth and into the void. Even so, it’s much more than we’d know what to do with, and only about 1% of it is enough to keep all the plants on Earth alive.

Energy is never lost or created, but transformed from one ‘flavor’ into another. Still, not all of them are equal, and heat seems to be the baseline that all others eventually degrade into. The Sun, therefore, gets quite hot.

Just how hot?

It depends on a lot of factors — mostly on exactly where you’re taking the measurement. There’s a lot of variation here.

First off is the Sun’s core. Here is where the fusion reaction that drives the star actually takes place. Due to the sheer mass of gas pressing down on the core, ambient pressure here is immense. Temperatures, too, are extremely high, due to how compressed everything gets. This is ideal, because such extreme conditions are needed for fusion to take place. To the best of our knowledge, temperatures at the core of the Sun can reach in excess of 15 million °C (27 million °F), which is a lot.

Image credits NASA, edited for clarity.

The next layer of the star is its ‘radiative zone’. Energy from the core moves out to this area, carried by bodies of superheated, ionized atoms, where it becomes trapped. It spends up to 1 million years here, before finally managing to escape the strong gravity and electromagnetic fields and reach the convective zone. This zone represents the upper layer of the Sun’s core, and temperatures here are believed to be around 2 million °C (3.5 million °F).

Hot plasma from this convective zone can bubble up towards the surface of the Sun. The next layer it encounters is the photosphere, which is about 5,500 °C (10,000 °F), significantly cooler compared to the previous layer. It is here that the radiation produced inside the star can first be perceived as light by an outside observer. A photosphere (‘sphere of light’ in ancient Greek) is defined as the deepest region of a light-emitting body that is still transparent to photons of certain wavelengths. In other words, the photosphere starts where the Sun’s plasma becomes transparent enough for light to be able to escape it.

However, the photosphere is not uniform. Areas of intense electromagnetic activity produce sunspots, which are darker and cooler than their surroundings; temperatures in the center of a sunspot can drop to lows of 4,000 °C (7,300 °F).

The next layer, the chromosphere (‘sphere of colors’ in ancient Greek), is a tad cooler, at about 4,320 °C (7,800 °F) on average. Light from this layer is thus dimmer, and we don’t usually see it. But, during a solar eclipse (when the moon covers the sun), this is the really fancy bit you see around its outline, the red rim surrounding the Sun. This color is emitted by the high content of hydrogen gas in the chromosphere.

In relative terms, temperatures in the photo- and chromatosphere aren’t that high — a candle, for example, burns at around 1,000 °C (1,800 °F). We know these two layers exist because their relatively mellow conditions allow for simple molecules such as water and carbon monoxide to survive, and we’ve picked up on their spectral emissions.

Lastly, there is the corona — the Sun’s crown. A bit unexpectedly, temperatures shoot back up in this layer, despite it being the farthest away from the core. In fact, it has average temperatures at the same order of magnitude as the core, although they are still lower. These range between 1 million °C and 10 million °C (roughly 1.7 – 17 million °F), according to the National Solar Observatory (NSO). The corona and chromatosphere are kept separated from this layer by a transition zone of highly-ionized helium atoms. This is less of a hard boundary and more of a chaotic, ever-churning sea of clouds. The corona might be so hot due to ‘nanoflares‘, but we’re still unsure.

Beyond the corona lies the Sun’s extended atmosphere, the heliosphere, which is less of a layer per se and more of an area of influence that the Sun exerts. While emissions such as solar winds or flares can send super-heated, charged particles flying off from a star into its heliosphere, this is much cooler than the layers we’ve discussed previously. The main component of the heliosphere is magnetic, and it has a key part to play in forming the Sun’s shield around our solar system.

How do we know how hot it is?

False-color 3-layer composite from the TRACE satellite, showing the solar corona for a “moderately active Sun”. Red indicates regions with high temperatures and activity, blue and green for colder areas. Loops can be seen connecting the active areas. Image credits NASA via Wikimedia.

Sticking a thermometer in the Sun is, understandably, a bit tricky. So we’ve had to rely on indirect methods of measurement to tell exactly how hot it can become.

If you put a kettle on to boil, you’ll be able to feel heat coming from the water even after you take it off the stove. How much of it you will perceive depends a lot on how close you hold your hand to the water. This process relies on the radiative properties of electromagnetic energy. To keep it simple, particles start moving when they heat up, and this motion generates thermal radiation; infrared cameras pick up on this kind of radiation, for example. Our senses perceive it as heat.

One of the simplest and also least accurate ways of assessing the Sun’s temperature is our own senses. Sunlight can be really hot on a clear day. Considering the star is around 149 million kilometers away, it must be outputting a lot of thermal energy for it to reach all the way here. Still, researchers like numbers, especially accurate ones, so they did develop several other means of gauging the star’s temperature.

One approach uses the link between heat and the light coming from a body — because in physics, unlike life, being hotter automatically makes you brighter, too.

Thermal radiation is a kind of electromagnetic radiation, but so is light. In very broad terms, as long as the cause is temperature, the brighter an object glows, the hotter it is. Irons heating in a forge are a good example. The hue can help us determine this temperature exactly. Red light is cooler than yellow light which is cooler than blue, and so on. A yellow-flamed candle burns colder than the blue flames on your stove.

A series of photographs of the Sun taken roughly at the same time, showcasing how different wavelength intervals can carry more or less energy. The first on the left is filtered white (normal) light. Image credits NASA / GSFC / Solar Dynamics Observatory.

That’s the working principle. In practice it becomes more complicated since the Sun doesn’t output a single type (wavelength) of light, but a whole cocktail of wavelengths that mix and interact to create the final, white light we perceive. We use a device called a spectrograph to tease these colors apart into individual wavelengths. They work much like raindrops do when creating rainbows.

Once we break down sunlight like this, we can look at each individual color (wavelength) of light and determine what temperature is associated with it. Every wavelength carries different amounts of energy, so the final step is to average out their temperatures to determine the final ‘product’. Think of it like determining the energy level of the middle-most color by looking at each individual color present in sunlight.

Sunlight can also be used to determine the chemical composition of our star. Every stellar body emits light across multiple wavelengths. But these ’emission spectra’ also show very small, generally well-defined gaps, tight wavelength intervals where no light is emitted (or where light is being absorbed). This comes down to how atoms interact with radiation but, suffice to say, these gaps are extremely reliable signatures of certain elements. As long as you understand the trace each of them leaves on the emission spectrum, you can determine a body’s composition from the light it emits. We call these traces Fraunhofer lines.

Which extinction lines are present, as well as how well-defined they are, are influenced by temperature. As such, this step can help determine both the composition and temperature of a star.

Still, we said earlier that the photosphere is a hard boundary in regards to our perception of light — we can’t see below this limit. Spectroscopy, then, as well as other optical methods, can only help us determine temperatures down to this layer. At the same time, even if the corona is much hotter, it’s also significantly less bright than the photosphere, so it has a very small contribution to this type of measurement.

As for anything deeper than the photosphere? That’s more theoretical. It’s not pulled out of our assumptions, but it’s still a theoretical estimate. Temperature conditions inside the Sun are based on the idea that it is in a state of hydrostatic equilibrium. That is, that its gravity (inward pressure) and expansive (outward pressure) generated by nuclear fusion at the core cancel each other out. If they wouldn’t, the star would blow up or turn black holey, so it’s a solid starting point.

If you combine this with chemical readings from spectroscopy, and estimates of the star’s mass (also calculated or obtained indirectly), you can determine what temperatures should be at the core to keep it all stable. We also know from our efforts at making fusion happen on Earth that humongous pressures and temperatures are needed to convince hydrogen atoms to merge; the Sun does that on a monumental scale, every second.

This is all based on tried-tested-and-true methods and theorems regarding natural processes, so they are reliable, but they’re still just estimates. If you’re the kind of person that needs exact measurements and figures, talking about the Sun might not be the best hobby for you. But, if it makes you find a way to go there and actually stick a thermometer in the thing so we can all find out, I won’t complain.

Europe’s most powerful solar telescope lets us see its surface and spots up close

New images captured by the GREGOR telescope in Tenerife, Spain, are giving us an unique view of the surface of the sun.

Image credits KIS.

These are the highest-resolution images of our host star ever taken by a European telescope, according to the authors. The results definitely support that claim — they give us a stunning look at the shapes and movements of solar plasma and the eerie dark voids of sunspots.


Although GREGOR has been in operation since 2012, it underwent a major redesign this year and also suffered a temporary pause in activity due to the pandemic. Now it’s up and running again, and its new, improved systems allow it to spot details as small as 50 kilometers in size on the solar surface. It might not sound like much, but this is the highest resolution of any European telescope (and, relative to the sun’s diameter of 1.4 million kilometers, quite good).

“This was a very exciting but also extremely challenging project,” said Lucia Kleint, who led the upgrade efforts on GREGOR. “In only one year we completely redesigned the optics, mechanics, and electronics to achieve the best possible image quality.”

To give you an idea of the telescope’s new abilities, she describes the images it captured as “if one saw a needle on a soccer field perfectly sharp from a distance of one kilometer”.

A sunspot observed in high resolution by the GREGOR telescope at the wavelength 430 nm. Image credits KIS.

The sun isn’t a solid object with a static, solid contour. Rather, its surface is always roiling and churning with super-heated plasma. The new images from GREGOR show the twisting structures created on the star’s surface and the contrasting darkness of sunspots. Sunspots are areas on the solar surface where magnetic fields are extremely strong, generating a spike in local pressure which darkens the area.

The Sun photographed at 304 angstroms by the Atmospheric Imaging Assembly (AIA 304) of NASA's Solar Dynamics Observatory (SDO). This is a false-color image of the Sun observed in the extreme ultraviolet region of the spectrum. (NASA)

Staring at the Sun: What is the lifecycle of a typical star

Though a mundane stellar body in many respects, the Sun will throughout its existence give rise to life and ultimately snuff it out. This is the past, present and future of the Sun, a very typical star.

Looking at our star — the Sun — from a universal point of view, there is little extraordinary about this ball of hydrogen and helium. In terms of size, the Sun also around mid-range for a star, whilst the universe possesses much smaller stars, it also hosts stars that are up to 100 times larger. A typical example of a star in this mass range, and of its radius, and age, it sits at an average distance from the centre of its galaxy — the Milky Way.  

Yet, despite how mundane the Universe may see the Sun, it is impossible to overestimate the importance of the Sun to life on Earth. Without the energy it provides living things simply could not exist. We could not exist. When it dies, our planet, every on it, and likely our species, also dies. And as is fitting, the Sun dominates our solar system, possessing over 99% of its total mass. 

In a way, the fact that the Sun is a very average star is a boon for our understanding of the Universe and the stellar objects that inhabit it. We have good reason to believe that the properties we observe belonging to the Sun are shared by many stars of this kind, and in-turn we can learn much about its birth, life, and death by looking beyond it and to the galaxy’s wider population of stars. 

One thing that isn’t typical about our star is its isolation. The majority of stars exist in binary pairs, but our Sun sits alone. Or it did. Humanity has provided our star with a little company. 

The Parker Solar Probe, launched by NASA in 2018, marks the closest approach to the Sun by any man-made object. The probe’s mission, to bring us images of the Sun’s corona and data that will unlock many of the remaining mysteries held by our star. In turn, this will help us better understand our solar system’s place in the Universe. 

Thus, what better time to review what we already know about the Sun, our theories about its birth, the processes that proceed beneath its outer layers and its eventual fate — intrinsically and inseparably tied to our own. 

This is the story of our Sun; its past, present, and future. And our own.

Past: Gravitational Collapse and Ignition

What is a star?

The very simple answer is a self-gravitating ball of gas hanging in space, existing in hydrostatic equilibrium, so it neither collapses nor expands. Thus, the story of a star’s life is really the tale of competing forces; the inward force of gravity encouraging the star to collapse and the outward forces that combat this urge.

Just as a star’s death hinges on the final victory of this inward gravitational force, its birth also arises from gravitational collapse. But, in the case of this initial collapse–one that eventually leads to the ignition of the star and the nuclear burning of hydrogen that will define the vast majority of its life–gravity must overcome the kinetic energy of individual gas and dust molecules that compose the cloud that will collapse to form a star.

A protostar surrounded by the gas a dust from which it formed. This young protostar–HBC 1–will eventually join the Sun on the main sequence. (ESA/ Hubble)

These collapses occur in the coldest and densest regions of clouds of dust and gas that float between star systems — referred to as the interstellar medium (ISM). To give you a rough idea of how large these ISM clouds are, the Sun and the solar system are currently passing through a local ISM that is approximately 60 light-years across. Thus, even when a small pocket of gas begins to collapse within an ISM cloud, it can birth a whole cluster of stars — these areas are called interstellar nurseries. 

The precise point at which the relationship between kinetic energy resistance and gravitational influence tips so that in-fall becomes inevitable is defined by ‘Jeans Mass’ — named after British physicist James Jeans, who first calculated it. 

Arising from this collapsing region of the ISM is a contracting cloud fragment that will eventually become a protostar. It’s difficult to currently say much about this process. Despite the fact that we have discovered many stellar nurseries and active star-forming regions, because they are heavily obscured by gas and dust, it’s hard to discern what is actually occurring within them. Also, this has to be tempered with the fact that even this early stage of stellar evolution proceeds on a cosmic timescale, which dwarves our lifespans considerably. 

As the cloud collapses, it forms a fragment which also contracts. As it does so, it emits radiation causing a minimal rise in temperature. But, as that contraction continues and more and more molecules are densely packed into the fragment, this radiation is increasingly trapped as the gas cloud/fragment becomes opaque. This causes a rapid rise in temperature, with the fragment reaching between 2,000K to 3,000K after around a thousand years of collapse. 

The chain of events that will birth a main-sequence star is now underway, thus we can describe the fragment as a protostar at this point. When the temperature within the core of the protostar is sufficiently hot, nuclear fusion begins. The energy provided by this process halts further contraction — a star is born! 

This early star will likely be surrounded by a disc of gas and dust from which a system of planets and other smaller bodies will form. For our star and solar system, this whole process occurred around 4.6 billion years ago. 

The Present: Nuclear Fusion, Hydrogen Burning, and the Main Sequence

Where does the Sun’s energy come from? 

The easy answer to that question is ‘from the fusion of hydrogen to helium’ — whilst a star burns hydrogen in its core, it is referred to as a main-sequence star or as being ‘on the main sequence.’ The fact that we see so many stars on the main sequence tells us that stars will spend the majority of their lives in this phase — turning hydrogen to helium in their cores. And that is the stage in which we find our Sun now. 

The many faces of the Sun. The instruments aboard the Parker Solar Probe take images of our star across a variety of frequencies. (ESA)

The way in which nuclear fusion creates the energy that stars radiate can most easily be explained with Einstein’s mass/energy relationship, the world’s most famous equation E=mc². Not all of the mass contained within the parent atoms that enter into nuclear processes ends up in the daughter particles. This ‘missing mass’ is converted to energy which is radiated away by photons and to a lesser extent, neutrinos.

In addition to providing a large proportion of a star’s energy output, the fusion processes that occur within the core of a main-sequence star also serve another, arguably more important function — balancing it against gravitational collapse.

Our models of the Sun suggest that its temperature and pressure increase on the way to the central core, with temperatures only becoming great enough to allow nuclear fusion to proceed at the heart of our star and a region close to it. Because nuclear fusion is so dependant on temperature, the boundary of where nuclear reactions can and cannot occur is sharp. 

The method by which energy is transported around a star varies depending on a star’s mass. For a star with roughly the mass of the Sun, there is a lack of extreme temperature gradient present in more massive stars that allow convection in the core, but there is still some convection allowed in the outer layers — a so-called convective envelope. This means that the main form of energy transport within the Sun is radiative. 

Radiative pressure joins the gas pressure provided by the material that composes the star in granting the outward force that balances the star against gravitational collapse, thus maintaining the hydrostatic equilibrium.

The fusion of hydrogen to helium can occur via a number of chain reaction processes. Within the Sun and other stars of a similar mass, the proton-proton chain dominates these reactions, with the so-called ppI chain in particular accounting for 91% of the reactions in the Sun’s core.

In more massive stars the ppII or ppIII branches of the proton-proton chain may dominate, and in the hottest of cores, an alternative way of creating helium from hydrogen– the CNO cycle uses carbon, nitrogen and oxygen as catalysts to aid the fusion of four hydrogen atoms to create helium–plays a significant role in energy production and helium synthesis.

Of course, as the fusion of hydrogen into helium in the core of a star defines its time in the main sequence that leads to an obvious question; what happens when it is gone?

The Future: Red Giants and White Dwarfs

What happens when the hydrogen is gone?

At the time of its birth, the Sun’s mass was composed of roughly 70% hydrogen, 28% helium, and 2% metals (using the astronomer’s definition of a ‘metal’ which is any element heavier than helium). The hydrogen content would have been greater and the helium and metal content lower were the Sun not born from a gas and dust cloud created by the death of an earlier ‘purer’ star, and thus enriched with helium and metals created by thermonuclear processes within that precursor. 

The sky around W Hydrae–a red giant observed by the ALMA telescope in 2017. (Digitized Sky Survey)

Were the Sun to convert all of its hydrogen to helium, its lifetime would be roughly 70 billion years, but, hydrogen-burning actually ceases before this supply is completely exhausted–when the hydrogen in the core is all but gone. This means the Sun has a hydrogen-burning lifetime of around 10 billion years, which it is currently almost half-way through. During this period, the star will change very little, just brightening very slightly. After this period ends, the changes the star undergoes are extreme and violent. When our Sun goes through them in roughly 5.4 billion years, it will certainly mean the end of life on our planet.

Once the hydrogen in the Sun’s core is exhausted nuclear fusion there will cease. This means that much of the outward pressure supporting the star from gravitational collapse is also cut off. This results in the gradual contracting of the core — now rich in helium — and the conversion of gravitational energy to thermal energy. As a result of this temperature raise, nuclear burning will then begin in the outer layers surrounding the core — thus creating a shell of burning hydrogen. 

The core continues to heat up, reaching a temperature of around 10⁸ K, high enough for helium fusion to start there. This results in the creation of extremely short-lived beryllium atoms, and the formation of carbon via what is known as the triple-alpha process. 

As a result of a much higher luminosity at this stage, the burning of helium within the Sun’s core lasts for a much shorter period of time than the main sequence and the burning of hydrogen did. For our star, this stage should last around hundred-million years, the surface temperature of the Sun will fall to around 3000 K, but its radius will increase from anywhere between a hundred and a thousand times its current size. 

This spells doom for the solar system’s inner planets, Mercury and Venus and possibly our own home, the Earth. A debate currently rages as to whether Earth will be engulfed by this expansion or simply scorched by its proximity to the surface of our star. The stellar body that had once made life possible on this planet, will, during the course of its own death throes, conclusively end it.

As a result of the contraction of the core and the expansion of the outer layers, the gravity at these tenous outer-layers is much weaker than the gravity found at the core; a disparity that results in a strong stellar wind. This phenomenon starts to strip away a considerable proportion of the red giant’s mass.

MIRA A is an ancient star shedding its outer layers into space. Observations of this white dwarfgive astronomers a clue as to what our Sun will look like as its enters its final phase. (
ESO/S. Ramstedt (Uppsala University, Sweden) & W. Vlemmings (Chalmers University of Technology, Sweden)

Mass loss processes including stellar winds and possibly thermal pulses arising from shell helium burning give rise to the next stage in a star’s evolution. The star’s inner core finds itself surrounded by a bubble of gas and dust that has been given the name ‘planetary nebula’. This is a complete misnomer, as these clouds have nothing to do with planets, and it arises from the misidentification of an early example. 

The final stage of our Sun’s evolution is a white dwarf — a stellar remnant roughly the radius of the Earth that is simply the Star’s exposed core. The hot core, with a temperature of between 25,000–5000 K sits at the centre of a planetary nebula created from what was once its outer layers. Though this stage will represent the final phase of our Sun’s life, it is not the end for our star’s larger mass counterparts. 

At this point, the fact that the Sun has no binary partner plays a role in its fate. For stars in binary pairs, it is possible for the accretion of material from one star to the other to ‘kick-start’ further nuclear processes in the beneficiary. The Sun neither has a donor nor does it have a counterpart to donate material to.

As its fuel is exhausted, the stellar remnant that was once our Sun will not possess the mass necessary to trigger the fusion of heavier elements. Nor will it possess the mass to collapse to a black hole or even a neutron star. The Sun will simply fade away from view joining a vast population of almost invisible white dwarfs that astronomers estimate makes up around 10% of all the stars in the Milky Way. 

There is no explosive end for our Star. Its fuel exhausted, it drifts in space, a smouldering ember. A silent relic of what was once a powerful arbiter of life and death within its own solar system. 


Green. S. F., Jones. M. H, et al, ‘An Introduction to the Sun and Stars,’ Cambridge University Press, [2003].

Ryan. S. G., Norton. A. J., et al, ‘Stellar Evolution and Nucleosynthesis,’ Cambridge University Press, [2010].

Gamow. G., ‘The Birth and Death of the Sun,’ Dover, [2005/ Revised Edition].

Our Sun’s magnetic field might form a ‘deflated croissant’, says NASA

New research at NASA developed a new prediction for the shape of the heliosphere, the magnetic bubble encasing our Solar System. But their result is not at all similar to the comet-like shape we’ve envisioned so far — in fact, it’s more of a “deflated croissant”, the agency reports.

An updated model of the heliosphere (seen in yellow).
Credits: Opher, et al. / NASA.

Outer space may be void, but it’s not completely empty. Magnetic fields and ionized gases permeate the galactic stretches between stars, and this substance is called the interstellar medium. It’s pushed back by the solar system’s magnetic ‘shield’, the heliosphere, just like Earth is protected from solar radiation by its own magnetic field. Using new data obtained from NASA’s crafts, the agency has developed a new model to describe the shape of this heliosphere.

Pastry-like shield

The shape of the heliosphere has been a point of interest of researchers for quite some time now. Traditionally, it is believed to have a comet-like shape with a long tail and a rounded leading edge (the ‘nose’). We believed it to be shaped in this fashion due to the Solar System zipping around through space.

However, researchers are now proposing an alternate model — the deflated croissant.

The shape of this heliosphere is very difficult to measure from within (where we are). For starters, it’s much too large for our sensors to be able to pick it up: its edge is around ten billion miles from Earth, according to NASA. Our only sources of direct data regarding it come from the two Voyager spacecraft that are well on their way to deep space.

We do, however, study this structure indirectly by capturing charged particles incoming to Earth from distant parts of the galaxy (cosmic rays). Alongside radiation formed by the Sun, these bounce back from the heliosphere, changing their physical properties in the process — and by studying them we can infer data about the heliosphere. In essence, we use this radiation the way a radar uses radio waves. This process is the one used by NASA’s Interstellar Boundary Explorer, or IBEX.

The latest iteration of the heliosphere model produced by NASA draws on data from the Voyager spacecrafts, the Cassini mission (to Jupiter), and the New Horizons mission (to Jupiter and Pluto). Using data from several points of the solar system allowed them to sample different types of particles.

Artist’s recreation of how the heliosphere blocks out cosmic rays (bright streaks in the image).
Image credits: NASA’s Goddard Space Flight Center / Conceptual Image Lab.

“There are two fluids mixed together. You have one component that is very cold and one component that is much hotter, the pick-up ions,” said Merav Opher, a professor of astronomy at Boston University, director of the DRIVE Science Center at Boston University focused on the challenge, and lead author of the new research.

“If you have some cold fluid and hot fluid, and you put them in space, they won’t mix — they will evolve mostly separately. What we did was separate these two components of the solar wind and model the resulting 3D shape of the heliosphere.”

Modeling the behavior of these particles separately allowed the team to estimate the shape of the heliosphere. The end result was a “deflated croissant” shape, with a central body and two jets that trail chaotically behind it.

“Because the pick-up ions dominate the thermodynamics, everything is very spherical. But because they leave the system very quickly beyond the termination shock, the whole heliosphere deflates,” said Opher.

The shape of the heliosphere is of great academic interest, but its activity is a boon for us all. It blocks about 75% of incoming cosmic rays, which would otherwise make their way into the solar system. While our planet is protected by a magnetic field and an atmosphere, astronauts and spacecraft are not.

This shield then, despite being shaped like a disappointing pastry, may be the only thing that allowed us to ever get off the planet and into space without being deep-fried by radiation in the process.

By knowing more about the heliosphere, we can also better estimate which alien planets are candidates for life.

Spacecraft snaps the closest picture of the sun, finds weird ‘campfires’

The arrow points to so-called campfire features. Reserachers think these are actually nanoflares that help heat the sun’s corona. Credit: ESA.

Earlier this year, while the coronavirus was just a frightening omen confined to Wuhan, NASA and the European Space Agency (ESA) launched the Solar Orbiter. The spacecraft’s primary mission is that of studying the sun in unprecedented detail. While there is still much to do, the Solar Orbiter is already providing a delicious treat — the closest image of the sun yet.

“These unprecedented pictures of the Sun are the closest we have ever obtained,” said Holly Gilbert, NASA project scientist for the mission at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “These amazing images will help scientists piece together the Sun’s atmospheric layers, which is important for understanding how it drives space weather near the Earth and throughout the solar system.”

“We didn’t expect such great results so early,” said Daniel Müller, ESA’s Solar Orbiter project scientist. “These images show that Solar Orbiter is off to an excellent start.”

‘Campfires’ on the sun

This animation shows a series of views of the Sun captured with the Extreme Ultraviolet Imager (EUI) on ESA/NASA’s Solar Orbiter on May 30, 2020.

The Solar Orbit mission got off to a rocky start after the pandemic forced the mission control at the European Space Operations Center in Darmstadt, Germany to close down completely for more than a week. The lockdown coincided with the mission’s commissioning phase, a highly delicate period when all instruments on board the spacecraft have to be calibrated and extensively tested.

All but essential personnel had to work from home, but despite having to perform critical operations remotely, the space engineers were up to the task.

The spacecraft completed its commissioning just in time for its first close flyby of the sun on June 15. At that time, Solar Orbit was just 45 million miles away from the sun’s surface, and mission control snapped a picture using six imaging instruments — each of which studies a different aspect of solar activity.

For instance, the Extreme Ultraviolet Imager (EUI) recorded data that reveals solar features in unprecedented detail.

Some of these features include so-called “campfires” dotting the surface of the sun.

“The campfires we are talking about here are the little nephews of solar flares, at least a million, perhaps a billion times smaller,” said David Berghmans, an astrophysicist at the Royal Observatory of Belgium in Brussels and principal investigator of the Solar Orbit mission. “When looking at the new high-resolution EUI images, they are literally everywhere we look.”

Solar Orbiter spots ‘campfires’ on the Sun. Locations of campfires are annotated with white arrows. Credit: Solar Orbiter/EUI Team (ESA & NASA).

Berghmans and colleagues aren’t sure what these campfires are or what their role is, but they have some ideas. It’s possible, the researchers say, that these features are nanoflares — mini-explosions that may help heat the sun’s outer atmosphere, known as the corona.

The corona is about 300 times hotter than the sun’s surface. If that makes absolutely no sense to you, you’re not alone. This is one of the biggest paradoxes surrounding solar activity, which scientists are still trying to figure out. The Solar Orbit mission, along with NASA’s Parker Solar Probe, is tasked with dispelling this mystery.

So we’re eagerly awaiting our next data set,” said Frédéric Auchère, principal investigator for SPICE operations at the Institute for Space Astrophysics in Orsay, France. “The hope is to detect nanoflares for sure and to quantify their role in coronal heating.”

Besides these intriguing solar features, the spacecraft also revealed zodiacal light — a very faint light from the sun which is reflected off interplanetary dust. Normally, the bright face of the sun obscures zodiacal light, but the spacecraft’s Solar and Heliospheric Imager (SoloHi) captured a perfect zodiacal light pattern. To see it, the instrument reduced the brightness of direct light from the sun by a factor of one trillion.

The first images from the Solar and Heliospheric Imager, or SoloHI instrument, reveal the zodiacal light (the bright blob of light on the right protruding towards the center). Credit: Solar Orbiter/ESA/NASA.

Next, pictures captured by the Polar and Helioseismic Imager (PHI) shows the sun’s poles and mapped their magnetic field.

This animation shows a sequence of images from the Polarimetric and Helioseismic Imager (PHI) on ESA/NASA’s Solar Orbiter. PHI measures the magnetic field near the Sun’s surface and allows the investigation of the Sun’s interior. Credit: ESA/NASA.

All these images and much more, including videos and raw data, are available at the ESA website.

Jupiter will be very bright and visible tonight, as it comes closest to Earth

The largest planet in our Solar System will be shining bright tonight and in the early hours of Tuesday morning.

Jupiter, seen by the Juno spacecraft.
Image via Wikimedia.

According to NASA, the orange giant will be in ‘opposition’ to Earth — at its closest point to our home in its orbit. Its size and proximity should make it very easy to spot during this time, with only the Moon and Venus likely to out-do it in terms of shine.

The best time to spot it should be between midnight and 2 in the morning. Light-drenched environments such as big cities aren’t going to be the best viewing spots (although Jupiter, which will outshine stars, should still be visible from here).

Your local weather conditions will obviously also impact visibility. Most of the US is forecasted to see clear night skies on Monday. The forecast for Europe is a bit more uncertain, with central and Eastern Europe likely to see rain.

“When a planet is at opposition, it is the best time to look for it in the night sky. This is the point in its orbit when it’s closest to the Earth, making it appear brighter than other times of the year,” AccuWeather explains.

The term ‘opposition’ refers to two celestial bodies being on opposite sides of a third one, usually the star they orbit (in this case, the Sun).

If you like star (planet?) gazing, this isn’t the only treat you’re getting this month. Jupiter, the yellow slightly-smaller giant behind Jupiter, will also reach opposition on July 20. Comet Neowise, discovered in late March, will be putting on “Earth’s greatest cometary show in 13 years”. It will become visible starting with 12-13 July and be most visible on the 23rd, according to Forbes.

Neowise is brighter than Halley’s Comet was in 1986 at the moment, and will only get brighter as it nears the Sun.

So make sure to keep your eyes on the skies this month, and not miss the show that nature is putting on.

New study shows sunlight can inactivate SARS-CoV-2

Increasingly, it is being shown that COVID-19 tends to spread faster and easier indoor than outdoor.

Previous studies have demonstrated that SARS-CoV-2, the virus that causes COVID-19, is stable on surfaces for extended periods of time, under indoor conditions.

A research from China showed that coronavirus transmission still takes place despite changing weather conditions in different parts of the country — ranging from cold and dry to warm and humid. A study in Hong Kong using SARS-CoV-2 in a lab solution showed that increasing temperature decreased the amount of viable virus that could be detected. No infectious virus remained after 30 minutes at 56° Celsius and five minutes at 70°C was enough to inactivate the pathogen.

Now, a new study by researchers at the National Biodefense Analysis and Countermeasures Center, a government biodefense research laboratory created by the U.S. Department of Homeland Security, shows that natural sunlight can rapidly inactivate SARS-CoV-2 on surfaces.

The findings, which come with caveats, suggest that the potential for fomite transmission may be significantly reduced in outdoor environments exposed to direct sunlight.

Sunlight vs COVID

To evaluate the influence of simulated sunlight on the persistence of SARS-CoV-2 on surfaces, the researchers exposed concentrated virus suspended in either simulated human saliva or culture media and then dried on stainless steel coupons mounted in a chamber to a light spectrum designed to represent natural sunlight. The coupons were exposed to the simulated sunlight for differing exposures, ranging from 2 to 18 minutes, to allow estimation of the viral inactivation rate. For comparison, the researchers also exposed a series of contaminated coupons in the chamber with no simulated sunlight for 60 minutes.

The results showed that under levels of simulated sunlight representative of midday on the summer solstice at 40°N latitude (the 40th Parallel), 90% of infectious virus is inactivated every 6.8 minutes in simulated saliva dried on a surface and every 14.3 minutes in cultured media dried on a surface. Significant inactivation also occurred under lower simulated light levels but at a slower rate. Inactivation rates were near zero on the coupons not exposed to sunlight.

The inactivation rate of SARS-CoV-2 was approximately two-fold greater in simulated saliva than in culture media. However, the researchers say it is unclear if the viral concentrate in simulated salvia is representative of contaminated saliva from an infected individual. This is good news but do not assume that summer months will be safer.

Sunlight has been in the COVID-19 news cycle for another reason – it is a great natural source of vitamin D, which has several health benefits, including an increased resistance to infectious diseases. When it comes to COVID-19, research is limited but clinical trials have started in Spain and France to see if vitamin D improves outcomes for COVID-19 patients. Both studies are expected to end in July 2020. In the meantime, continue to take appropriate steps to protect yourself and those around you.

Highest-ever resolution images of the sun revealed

The highest-ever resolution images of the sun have been unveiled by a group of British scientists working alongside NASA researchers, proving that the atmosphere of the sun is much more complex than we thought.

Credit University of Central Lancashire

Analyzed by researchers at the University of Central Lancashire (UCLan) and collaborators from NASA’s Marshall Space Flight Centre, the images will now provide astronomers with a better understanding of the sun’s atmosphere.

Scorching glory

The images were taken by NASA’s High-Resolution Coronal Imager (Hi-C) telescope, carried into space on a sub-orbital rocket flight. The telescope can pick out structures in the sun’s atmosphere as small as 70km in size, or about 0.01% of the star’s total size.

Until now, certain parts of the sun’s atmosphere appeared dark or mostly empty, but the new images revealed strands that are about 500 kilometers (260 miles) in width with hot electrified gases flowing inside them.

“Until now, solar astronomers have effectively been viewing our closest star in ‘standard definition’, whereas the exceptional quality of the data provided by the Hi-C telescope allows us to survey a patch of the sun in ‘ultra-high definition’ for the first time,” Robert Walsh, professor of solar physics at UCLan, said in a statement.

Hi-C is a bit different from most telescopes since it’s launched on a sub-orbital rocket. On its last flight in 2018, Hi-C spent about five minutes snapping images of the sun from the edge of space. It returned to Earth through a parachute-assisted landing.

The exact physical mechanism that is creating these pervasive hot strands remains unclear, so the scientific debate will now focus on why they are formed, and how their presence helps us understand the eruption of solar flares and solar storms that could affect life on Earth.

Credit University of Central Lancashire

The international team of researchers is now planning to launch the Hi-C rocket mission again, this time overlapping their observations with two sun-observing spacecraft currently gathering further data, NASA’s Parker Solar Probe and ESA’s Solar Orbiter (SolO).

Amy Winebarger, Hi-C investigator at NASA’s Marshall Space Flight Center, said: “These new Hi-C images give us a remarkable insight into the Sun’s atmosphere. Along with ongoing missions such as Probe and SolO, this fleet of space-based instruments in the near future will reveal the Sun’s dynamic outer layer in a completely new light.”

Tom Williams, a postdoctoral researcher at UCLan who worked on the Hi-C data, said in a statement that the images would help provide a greater understanding of how the Earth and sun-related to each other.

“This is a fascinating discovery that could better inform our understanding of the flow of energy through the layers of the sun and eventually down to Earth itself,” he said. “This is so important if we are to model and predict the behaviour of our life-giving star.”

The research has been published in the Astrophysical Journal.

Astronomers capture the most detailed image of the sun

In what could be a key step to solve several long-standing mysteries around it, a group of astronomers have released the highest resolution image of the sun, obtained thanks to observations by the Inouye solar telescope in Hawaii.

This is the highest resolution image of a star yet. Credit: NSO/NSF/AURA.

The images show a never-before-seen level of structure hidden within the plasma exterior. This was achieved thanks to the telescope’s 30km resolution, which is more than twice that of the next best solar observatories around the world. The telescope is located at a 3,000 meters volcano on the island of Maui.

“These are the highest resolution images of the solar surface ever taken,” said Thomas Rimmele, the director of the Inouye solar telescope project. “What we previously thought looked like a bright point – one structure – is now breaking down into many smaller structures.”

A close-up of the solar telescope’s first image of the sun. Credit: NSO/NSF/AURA.

The solar telescope revealed the sun’s surface to be speckled with granular structures, each the size of France. At the center of each grain, there are rising columns of plasma, heated to almost 6,000ºC (10,800F). When the plasma cools, it goes back below the surface through channels between the granular structures.

The surface of the sun in motion. Credit: NSO/NSF/AURA.

Valentin Pillet, the director of the National Solar Observatory, described the challenges that involved taking the solar images. Keeping the telescope’s mirror at ambient temperature while looking at the sun proved difficult, as temperature deviation causes air turbulences that can alter the images.

A closeup of the features captured by the Inouye solar telescope, showing the vast scale of the sun. Credit: NSO/NSF/AURA.

At the same time, Pillet said that in order to carry out the project they emptied a swimming pool worth of ice into eight tanks every day. Then, during the day, coolant was routed through the ice tanks and distributed through the pipes of the observatory. They also positioned 100 air jets behind the main mirror.

The experts at the observatory also deflected the incoming sunlight from the primary mirror into a chamber of mirrors, located below the dome. The light was then bounced from mirror to mirror. The observatory is equipped with a full set of instruments, which will allow measuring the magnetic field from the surface of the sun later in the year.

Such observations will help to solve long-standing mysteries around the sun, such as why its atmosphere is heated to millions of degrees when the surface is 6,000ºC. Understanding the physics behind the solar flares will be able to improve the ability to predict space weather.

“On Earth, we can predict if it is going to rain pretty much anywhere in the world very accurately, and space weather just isn’t there yet,” said Matt Mountain, president of the Association of Universities for Research in Astronomy. “What we need is to grasp the underlying physics behind space weather, and this starts at the Sun, which is what the Inouye Solar Telescope will study over the next decades.”

When will the Sun run out of fuel?

All life on Earth owes its existence to the Sun, whose rays have showered the planet with energy for billions of years. But, like all things, the Sun has its days numbered. Every star has a life cycle consisting of formation, main sequence, and ultimately death when it runs out of fuel — the Sun is no exception.

The good news is that before this will happen, our species should have evolved into something entirely different or long become extinct. According to scientists, the sun has enough fuel to keep it running for another 5 billion years. When that happens, the solar system will be transformed forever.

The life cycle of the Sun

Credit: Socratic.

The star is classed as a G-type main-sequence star, also known as a yellow dwarf. Like other G-type main-sequence stars, the Sun converts hydrogen to helium in its core through nuclear fusion. Each second, it fuses about 600 million tons of hydrogen to helium. The term yellow dwarf is a misnomer since G stars actually range in color from white to slightly yellow. The Sun is, in fact, white but appears yellow because of Rayleigh scattering caused by the Earth’s atmosphere.

The Sun and its planets have been around for about 4.57 billion years. They were all formed out of the same giant cloud of molecular gas and dust which, at some critical point, collapsed under gravity at the center of the nebula.

Due to a nonuniform distribution of mass, some pockets were denser, consequently attracting more and more matter. At the same time, these clumps of matter that were increasing in mass began to rotate due to the conservation of momentum. The increasing pressure also caused the dense regions of gas and dust to heat up.

Scientists’ models suggest that the initial cloud of dust and gas eventually settled into a huge ball of matter at the center, surrounded by a flat disk of matter. The ‘ball’ would eventually turn into the Sun once the temperature and pressure were high enough to trigger nuclear fusion, while the disk would go on to form the planets.

Scientists estimate that it took the Sun only 100,000 years to gather enough mass in order to begin fusing hydrogen into helium. For roughly a few million years, the Sun shone very brightly as a T Tauri star, before it eventually settled into its current G-type main-sequence configuration.

Like most other stars in the universe, the Sun is currently living through its ‘main sequence’ phase. Every second, 600 million tons of matter are converted into neutrinos and roughly 4 x 1027 Watts of energy. 

What happens to Earth after the sun dies

There is only a finite amount of hydrogen in the Sun which means it must eventually run out. Since its formation, scientists estimate the Sun consumed as much hydrogen as about 100 times the mass of the Earth.

As the Sun loses hydrogen, its fuel-holding core shrinks, allowing the outer layers to contract towards the center. This puts more pressure on the core, which responds by increasing the rate at which it fuses hydrogen into helium. Naturally, this means the Sun will get brighter with time.

Scientists estimate that the Sun’s luminosity increases by 1% every 100 million years. Compared to when it turned into a G-type main-sequence star 4.5 billion years ago, the Sun is now 30% more luminous.

All of this means that the Sun will slowly turn the heat up on Earth. About 1.1 billion years from now, the Sun will be 10% brighter, triggering a greenhouse effect on Earth similar to the warming that made Venus into a hellish planet.

As the Sun approaches the end of its life cycle, Earth’s ocean will boil and the planet will become uninhabitable as early as 1 billion years from now. Credit: Wikimedia Commons.

The heat transfer with Earth’s atmosphere would be huge by this point in time, causing the oceans to boil and the ice caps to melt. As the atmosphere becomes saturated with water, high energy radiation from the Sun will split apart the molecules, allowing water to escape into space as hydrogen and oxygen until the whole planet becomes a barren wasteland.

Life would stand no chance, permanently sealing Earth’s fate as the next Venus or Mars. Speaking of which, at this point into the future, Mars’ orbit would move into the habitable zone, which might become a second Earth for a short while before it too would become unsalvageable.

Some 3.5 billion years from now, the Sun will be 40% brighter than today.

And, in about 5.4 billion years, the Sun will run out of hydrogen fuel, marking the end of its main sequence phase. What will inevitably happen next is that the built-up helium in the core will become unstable and collapse under its own weight. Since the Sun first started fusing hydrogen, all of the helium it has produced has accumulated in the core with no way to get rid of it.

At this point, the Sun will be ready to enter its “Red Giant” phase, characterized by an enormous swelling in size due to gravitational forces that compress the core and allow the rest of the sun to expand. The Sun will grow so large that it will encompass the orbits of Venus and Mercury, and quite possibly even Earth. Some astronomers estimate it might grow to 100 times its current size.

What this means is that even if life on Earth somehow miraculously survives the tail-end of the Sun’s main sequence, it will most certainly be destroyed by a Red Sun so large it will touch our planet.

Don’t be blue, even stars have to die

The Sun will remain in a Red Giant phase for about 120 million years. At this point, the core of the Sun, when it reaches the right temperature and pressure, will start fusing helium into carbon, then carbon and helium into oxygen, neon and helium into magnesium, and so on all the way up to iron. This reaction is triggered when the last remaining shell of hydrogen that envelops the core is burned.

The Sun will then eventually expel its outer layers and then contract into a white dwarf. Meanwhile, all the Sun’s outer material will dissipate, leaving behind a planetary nebula.

“When a star dies it ejects a mass of gas and dust – known as its envelope – into space. The envelope can be as much as half the star’s mass. This reveals the star’s core, which by this point in the star’s life is running out of fuel, eventually turning off and before finally dying,” explained astrophysicist Albert Zijlstra from the University of Manchester in the UK.

“It is only then the hot core makes the ejected envelope shine brightly for around 10,000 years – a brief period in astronomy. This is what makes the planetary nebula visible. Some are so bright that they can be seen from extremely large distances measuring tens of millions of light years, where the star itself would have been much too faint to see.”

Cat’s Eye Nebula. Credit: NASA/ESA.

If it were much more massive, the Sun’s final fate would have been much more spectacular exploding into a supernova and perhaps forming a black hole. Due to its relatively small size, however, the Sun will likely live as a white dwarf for trillions of years before finally fading away entirely leaving the solar system in pitch-black darkness. The Sun has now become a black dwarf.

In summary: the sun has about 5-7 billion years left of its main sequence phase — the most stable part of its life. However, life on Earth might become extinct as early as 1 billion years from now due to the Sun becoming hot enough to boil the oceans.

NASA’s Parker Solar Probe Could Help Solve One of the Mysteries of Our Sun

Artist rendering of NASA's Parker Solar Probe observing the sun. Credit: NASA/Wikimedia Commons.

Artist rendering of NASA’s Parker Solar Probe observing the sun. Credit: NASA/Wikimedia Commons.

One of the most logically-baffling solar mysteries is the fact that the sun’s surface is close to 10,000 degrees Fahrenheit while its outer atmosphere is several million degrees hotter. The body of the heat’s source itself is cooler than the atmosphere surrounding the fireball — and that’s simply against the common sense of physics.

Some physicists think that the terrific, intense heat displayed in the outer limits of the sun’s atmosphere may be explained by magnetic waves traveling to and from the solar surface, bouncing off the upper atmosphere (otherwise known as the corona) of the star. Recent studies have suggested that this activity could be tied to the sun’s zone of preferential ion heating. In this zone, ions reach scorching temperatures exceeding those at the very core of the sun.

Another element which has a role to play in this outlying solar vortex are Alfven waves. These waves are low-frequency oscillations traveling through a plasma in a magnetic field. Scientists think that these waves are making solar wind particles to collide and ricochet off one another. But once it hits the outskirts of the zone of preferential heating, the solar wind sweeps by at an extremely fast pace. Thus, it manages to evade the Alfven waves from there on out.

Researchers at trying to definitively mark the extent to which the superheating effect reaches beyond the sun. Recent research has brought light to a connection between the Alfven point (the point of altitude beyond the solar surface that permits solar wind particles to break free of the sun) and the outskirts of the zone of preferential heating. These two fields have fluctuated in unison. They shall continue their dance, and in 2021, NASA’s Parker Solar Probe, christened in honor of physicist Eugene Parker, should come in contact with the two boundaries.

The spacecraft includes instruments capable of recording a number of significant data pertaining to those solar fields. The information it would collect in some two years to come would be invaluable in this particular study.

The Parker Solar Probe was launched in August 2018. It made its second successful fly-by of our sun in early April with the follow-up perihelion (the point at which it gets closest to the sun) scheduled to occur on September 1. Visit NASA’s page on the Parker Solar Probe to learn more about it and its mission. To learn of interesting updates, check out the website of Parker Solar Probe Science Gateway.

Giant CME.

Researchers spot the first coronal mass ejection outside our solar system — it was massive

An international team of researchers has managed to identify the first coronal mass ejection, or CME, in a star other than our Sun.

Giant CME.

Image credits NASA / GSFC.

An intense flash of X-rays, followed by the bursting on an immense bubble of plasma — that’s what researchers led by Costanza Argiroffi, a researcher at the University of Palermo and associate researcher at the National Institute for Astrophysics in Italy, have seen in the corona of HR 9024, an active star about 450 light-years away from us. This is the first CME ever spotted in a star outside our solar system.

The findings help us better understand how CME fits into the lives of active stars across the Universe and will help us systematically study such dramatic events in the future.


“The technique we used is based on monitoring the velocity of plasmas during a stellar flare,” said Costanza Argiroffi. “This is because, in analogy with the solar environment, it is expected that, during a flare, the plasma confined in the coronal loop where the flare takes place moves first upward, and then downwards reaching the lower layers of the stellar atmosphere.”

“Moreover, there is also expected to be an additional motion, always directed upwards, due to the CME associated with the flare.”

The team used data collected by NASA’s Chandra X-ray Observatory to analyze a “particularly-favorable” flare, according to a Chandra Observatory press release. Solar flares are sudden, quite violent events, during which a star’s brightness increases substantially. Flares are sometimes, but not always, associated with CMEs.

The High-Energy Transmission Grating Spectrometer (HETGS) device aboard Chandra is the only instrument we have at our disposal so far that can be used to measure the movement of matter involved in CMEs. CMEs involve the expulsion of plasma — very hot, electrically-charged gas — in a star’s corona (atmosphere), at speeds of up to tens of thousands of miles per hour.

CMEs are only produced in magnetically-active stars, the results confirm. The findings also support the validity of what we know about CMEs so far, for example, that material involved in a flare is very, very hot (from 18 to 45 million degrees Fahrenheit), and that it first rises and then drops with speeds between 225,000 to 900,000 miles per hour.

“This result, never achieved before, confirms that our understanding of the main phenomena that occur in flares is solid,” said Argiroffi. “We were not so confident that our predictions could match in such a way with observations, because our understanding of flares is based almost completely on observations of the solar environment, where the most extreme flares are even a hundred thousand times less intense in the X-radiation emitted.”

The “most important” discovery, however, is that after the flare a body of much cooler plasma (of around 7 million degrees Fahrenheit) rises from the star’s body with “a constant speed of about 185,000 miles per hour,” adds Argiroffi. Such a result is “exactly what one would have expected for the CME associated with the flare.”

The team adds that, based on Chandra’s readings, the mass of the CME in questions was roughly two billion pounds. This would make it about ten thousand times as massive as the largest CMEs put out by the Sun. This last tidbit reinforces the idea that more magnetically active stars generate larger-scale versions of solar CMEs.

“The observed speed of the CME, however, is significantly lower than expected. This suggests that the magnetic field in the active stars is probably less efficient in accelerating CMEs than the solar magnetic field,” Argiroffi concludes.

The paper “A stellar flare−coronal mass ejection event revealed by X-ray plasma motions” has been published in the journal Nature.

Plasma globe.

Solar plasma observations bring us one step closer to stable fusion generators

An international research effort brings us one step closer to unlocking fusion power on Earth.

Plasma globe.

A plasma globe toy.
Image via Pixabay.

The team of researchers, comprised of members from Ireland and France, used ground-based radio telescopes and ultraviolet cameras mounted on a NASA spacecraft to peer into the unseen workings of the Sun. Their observations give us a better understanding into how and why plasma becomes unstable. With this data in hand, researchers will hopefully be able to better control plasma down on Earth and potentially tame it into a clean, safe, and extremely powerful energy source.

Abundant, but not with us

“We worked closely with scientists at the Paris Observatory and performed observations of the Sun with a large radio telescope located in Nançay in central France,” says Dr. Eoin Carley, a postdoc at Trinity College Dublin and the Dublin Institute of Advanced Studies (DIAS), who led the research

“We combined the radio observations with ultraviolet cameras on NASA’s space-based Solar Dynamics Observatory spacecraft to show that plasma on the sun can often emit radio light that pulses like a light-house. We have known about this activity for decades, but our use of space and ground-based equipment allowed us to image the radio pulses for the first time and see exactly how plasmas become unstable in the solar atmosphere.”

We’re used to thinking of matter as predominantly being gaseous, liquid, solid, and a smattering of other rare and exotic states. That might be the case on Earth, but in the Universe at large, plasma is definitely the most abundant state of matter. Stars are huge things, and they’re mostly plasma, for example — our Sun included.

Plasma is a very energetic, very unstable electrically charged fluid. Conditions on our planet are simply too tame for it to pop up, so it’s extremely scarce and hard to study. Specialized laboratories that can recreate the extreme conditions of space are needed to properly study it. However, the team came up with a better plan: to just look at what the huge ball of plasma in the sky is doing. The Sun, they argue, gives us a chance to study how this state of matter behaves in conditions that are too extreme for any laboratory we’ve ever built.

“The solar atmosphere is a hotbed of extreme activity,” Dr. Carley adds, “with plasma temperatures in excess of 1 million degrees Celsius and particles that travel close to light-speed. The light-speed particles shine bright at radio wavelengths, so we’re able to monitor exactly how plasmas behave with large radio telescopes.”

The team used radio telescopes across Europe and ultraviolet cameras mounted on NASA spacecraft to observe solar plasma and compare its behavior to that of plasma we’ve generated. They hope that their data will help us design efficient magnetic confinement systems for our fusion reactors — these are the things that will keep plasma from liquefying out reactors’ walls. Successfully designing a working fusion reactor wouldn’t be a mean feat at all; these reactors are miles ahead of our current tech in terms of output, safety, and cleanliness.

“Nuclear fusion is a different type of nuclear energy generation that fuses plasma atoms together,” says Professor at DIAS and collaborator on the project, Peter Gallagher, “as opposed to breaking them apart like fission does. Fusion is more stable and safer, and it doesn’t require highly radioactive fuel; in fact, much of the waste material from fusion is inert helium.”

“The only problem is that nuclear fusion plasmas are highly unstable. As soon as the plasma starts generating energy, some natural process switches off the reaction. While this switch-off behaviour is like an inherent safety switch — fusion reactors cannot form runaway reactions — it also means the plasma is difficult to maintain in a stable state for energy generation. By studying how plasmas become unstable on the Sun, we can learn about how to control them on Earth.”

The paper “Loss-cone instability modulation due to a magnetohydrodynamic sausage mode oscillation in the solar corona” has been published in the journal Nature Communications.


Jupiter formed far from the sun and traveled closer during its early days

Jupiter traveled a bit in its youth, evidence from asteroids around the planet reveals. This brown gas giant formed four times as far away from the sun than the orbit it’s currently on and inched closer over the last 700,000 years.


Jupiter and its moon Io.
Image via Pixabay.

New research led by members from the Lund University is revealing Jupiter’s wandering past based on the company it keeps. Using computer simulations to look at the distribution of near-Jupiter asteroids called Trojans, the team reports that their current layout in space can only be explained by Jupiter forming far away and then migrating to a closer orbit around the sun.

The prodigal son

“This is the first time we have proof that Jupiter was formed a long way from the sun and then migrated to its current orbit,” explains Simona Pirani, doctoral student in astronomy at Lund University, and the lead author of the study. “We found evidence of the migration in the Trojan asteroids orbiting close to Jupiter.”

Gas giants, as a rule of thumb, orbit pretty close to their host stars. To the best of our knowledge. that’s not where they form, however — these ponderous bodies of gas accrete further away and then migrate closer to the star.

In order to find out if Jupiter behaved the same way, Pirani’s team used computer simulations to estimate its movements over the past 4.5 billion years. The solar system was quite young in that day, its planets freshly-minted from the primordial dust which circled around the sun in a disk. At that time, 4.5 billion years ago, Jupiter was no larger than our own planet, the team reports.

It was also four times further away from the sun that it is now.

The Trojans Pirani talks about consist of two groups of thousands of asteroids that float around roughly on the same orbit as Jupiter — one group a bit in front and the other a bit behind the planet’s exact orbit. There are also 50% more Trojans in front of Jupiter rather than behind it, the team explains, a feature which helped them understand how the planet migrated over time.

“The asymmetry has always been a mystery in the solar system,” says Anders Johansen, professor of astronomy at Lund University and one of the paper’s co-authors.

We never really understood why there were more Trojans in front of Jupiter rather than behind it up to now. The team’s simulations suggest this happened because Jupiter gradually corralled in asteroids as it moved towards the sun. Based on the ratio between the two bodies of Trojans, the team says Jupiter likely formed four times farther out in the solar system than it is today. During its journey towards the sun, the planet’s gravity then drew in more Trojans in front of it than behind it.

According to their study, Jupiter’s migration took around 700,000 years, roughly 2-3 million years after it first started accreating. It moved closer to the center of the solar system on a spiral trajectory, as Jupiter orbited the sun in on increasingly tight orbit, goaded on by shifting gravitational forces from the gases surrounding the Sun, the team says.

The Trojans joined Jupiter while it was still a young planet — just a solid core without any atmosphere. This suggests that the Trojans are probably hewn of the same (or similar) matter that formed Jupiter’s core. NASA’s upcoming Lucy mission (scheduled for 2021) will allow the team a closer look at the Trojans.

“We can learn a lot about Jupiter’s core and formation from studying the Trojans,” says Anders Johansen.

The authors believe that the gas giant Saturn and ice giants Uranus and Neptune could have migrated in a similar way to Jupiter during their history.

The paper “Consequences of planetary migration on the minor bodies of the early solar system” has been published in the journal Astronomy & Astrophysics.


Massive solar storms are naturally-recurring events, study finds — and we’re unprepared for them

Solar storms can be even more powerful than what our measurements so far have indicated — and we’re still very unprepared.


Image via Pixabay.

Although our planet’s magnetic field keeps us blissfully unaware of it, the Earth is constantly being pelted with cosmic particles. Sometimes, however — during events known as solar storms, caused by explosions on the sun’s surface — this stream of particles turns into a deluge and breaks through that magnetic field.

Research over the last 70 years or so has revealed that these events can threaten the integrity of our technological infrastructure. Electrical grids, various communication infrastructure, satellites, and air traffic can all be floored by such storms. We’ve seen extensive power cuts take place in Quebec, Canada (1989) and Malmö, Sweden (2003) following such events, for example.

Now, new research shows that we’ve underestimated the hazards posed by solar storms — the authors report that we’ve underestimated just how powerful they can become.

‘Tis but a drizzle!

“If that solar storm had occurred today, it could have had severe effects on our high-tech society,” says Raimund Muscheler, professor of geology at Lund University and co-author of the study. “That’s why we must increase society’s protection again solar storms.”

Up to now, researchers have used direct instrumental observations to study solar storms. But the new study reports that these observations likely underestimated how violent the events can become. The paper, led by researchers at Lund University, analyzed ice cores recovered from Greenland to study past solar storms. These cores formed over the last 100,000 years or so, and have captured evidence of storms over that time.

According to the team, the cores recorded a very powerful solar storm occurring in 600 BCE. Also drawing on data recovered from the growth rings of ancient trees, the team pinpointed two further (and powerful) solar storms that took place in 775 and 994 CE.

The result thus showcases that, although rare, massive solar storms are a naturally recurring part of solar activity.

This finding should motivate us to review the possibility that a similar event will take place sooner or later — and we should prepare. Both the Quebec and Malmö incidents show how deeply massive solar storms can impact our technology, and how vulnerable our society is to them today.

“Our research suggests that the risks are currently underestimated. We need to be better prepared,” Muscheler concludes.

The paper “Multiradionuclide evidence for an extreme solar proton event around 2,610 B.P. (∼660 BC)” has been published in the journal Proceedings of the National Academy of Sciences.

Credit: NASA.

NASA spacecraft beams back first image from inside the Sun’s atmosphere

NASA scientists treated the audience at this week’s American Geophysical Union meeting to a special treat: an unprecedented photo taken from inside the sun’s atmosphere. The image was captured by the Parker Solar Probe, which recently broke the record for the closest man-made contraption to orbit the sun, but also for the fastest spacecraft ever.

Credit: NASA.

Credit: NASA.

When it took this breathtaking photo, Parker was a mere 27.1 million km (16.9 million miles) from the sun, effectively traveling through its corona — the outermost part of the Sun’s atmosphere. The temperature in the corona is more than a million degrees, surprisingly much hotter than the temperature at the Sun’s surface which is around 5,500° C (9,940° F or 5,780 kelvins). It’s quite formidable that something we’ve made is capable of withstanding such elements — let alone able to beam back valuable data or images such as this.

Normally, we cannot see the corona directly because the sun’s surface is far too bright, overpowering the fainter corona. It’s possible sometimes to see a wispy corona with the naked eye during a solar eclipse, when the moon blocks the solar surface. Otherwise, scientists use a special instrument called a coronagraph, which is equipped on some ground-based telescopes and satellites.

Two views of the Sun's corona: during an eclipse (top) and in ultraviolet light (bottom). Credit: NCAR's High Altitude Observatory and NASA SDO.

Two views of the Sun’s corona: during an eclipse (top) and in ultraviolet light (bottom). Credit: NCAR’s High Altitude Observatory and NASA SDO.

This particular image was radioed back to Earth on December 7, however, it was taken much earlier, in November. The complete dataset won’t be sent until Parker undergoes a second flyby in April 2019.

The two distinct jets seen emanating from the left of the image are known as coronal ejections, which are streams of plasma that often follow solar flares. The bright spot in the distance is Jupiter, the gas giant. What about those black spots? Those are far less interesting because there’s nothing there in reality — just artifacts of background correction.

Parker also broke the record for the fastest spacecraft ever, beating the previous record set by Helios 2 in 1976 at 246,960 kilometers per hour (153,454 miles per hour) relative to the sun. But during its final pass around the sun, Parker is expected to reach a staggering top speed of 692,017 km/h (430,000 mph). This will actually be important since Parker will be able to match the rotational speed of the sun, enabling the probe to hover over the same region of the sun for a brief period of time — just like a geosynchronous satellite.

For its mission, Parker carries a range of instruments that can study the sun both remotely and in situ (directly) — the kind of observations that might unravel some of the sun’s most well-kept secrets. One of them has to do with the mystery of the acceleration of solar wind — the constant ejection of magnetized material from the sun. Somewhere, somehow, this solar wind is accelerated to supersonic speeds, and scientists don’t know why yet.

Perhaps the most mind-boggling thing about the sun is that its atmosphere is thousands of times hotter than its surface, which makes no sense. But perhaps Parker can come up with an answer.

During its closest flyby, slated for June 2025, Parker will be only 6.1 million kilometers (3.8 million miles) from the sun’s surface, where temperatures can reach millions of degrees Celsius. Meanwhile, Parker will complete 24 orbits, looping between Venus and the Sun.