Tag Archives: red dwarf

Gallery of stellar winds around cool ageing stars, showing a variety of morphologies, including disks, cones, and spirals. The blue colour represents material that is coming towards you, red is material that is moving away from you. (L. Decin, ESO/ALMA)

How Stellar Winds of Dying Stars Are Shaped

New observations have revealed that stellar winds are not spherical as previously believed, but instead come in a variety of shapes that resemble those of planetary nebulae — created when a dying star explosively sheds its outer layers, which by a weird naming quirk actually have nothing to do with planets.  In fact, those winds could mark out the ‘molds’ by which planetary nebulae are shaped.

The discovery comes as a result of research conducted by a team of astronomers including Leen Decin, from the Institute of Astronomy, KU Leuven, and is detailed in a paper published today in the journal Science. “We noticed these winds are anything but symmetrical or round,” Decin says. “Some of them are actually quite similar in shape to planetary nebulae.”

Gallery of stellar winds around cool ageing stars, showing a variety of morphologies, including disks, cones, and spirals. The blue colour represents material that is coming towards you, red is material that is moving away from you. (L. Decin, ESO/ALMA)
Winds of red giant stars observed around Gamma Aquilae
[Credit: Decin et al., Science (2020)] (L. Decin, ESO/ALMA)

The team believes that this variety in stellar winds and planetary nebulae shape around dying stars are connected and a result of interactions with companion stars in binary pairings, or even from exoplanets in orbit around the stars. “The Sun — which will ultimately become a red giant — is as round as a billiard ball,” Decin explains. “So we wondered; how can such a star produce all these different shapes?”

The findings collected by the team could explain a long-standing mystery of planetary nebulae around stellar remnants like red dwarfs come in a variety of close-but-not-quite-spherical shapes. 

Planetary nebulae display such a wide range of complex shapes and structures that although the influence of binary companions has been suggested as a possible cause of this diverse range of asymmetric forms, the fact they can arise around stars with spherically symmetric stellar winds has, until now, remained unexplained.

The answer found by the team is that these winds aren’t symmetric at all and that the shape of the winds directly informs the shape of planetary nebulae. 

Dying Stars’ Companions are a Bad Influence

The observations of the stellar winds of 14 AGB stars using the Atacama Large Millimeter/submillimeter Array made by the team were so-detailed that they actually allowed the team to categorize the shapes of the stellar winds and planetary nebula. Some were disc-shaped, some contained spirals, and some were conical — a good indication that the shapes were not created randomly — but, none had spherical symmetry.

Gallery of stellar winds around cool ageing stars, showing a variety of morphologies,
including disks, cones, and spirals. The blue colour
represents
material that is coming towards you, red
is material that is moving away from you. (L. Decin, ESO/ALMA)

In fact, the team realized it was the presence of other low-mass stars or exoplanets in the vicinity of the primary star that was shaping the stellar wind and planetary nebula. Professor Decin is on hand to provide a useful and colorful analogy: “Just like how a spoon that you stir in a cup of coffee with some milk can create a spiral pattern, the companion sucks material towards it as it revolves around the star and shapes the stellar wind.”

Stellar winds are important to astronomers as they account for one of the main mechanisms by which stars lose mass. This mechanism becomes even more critical when attempting to understand the death throes of stars of similar sizes to the Sun and as their cores contract and the outer layers swell creating planetary nebulae — the other major contributor to mass-loss in aging stars. Discovering the role played by stellar companions in such a process is a surprise, to say the least. 

The stellar wind of R Aquilae resembles the structure of rose petals. (L. Decin, ESO/ALMA)

“All our observations can be explained by the fact that the stars have a companion,” says Decin. “Our findings change a lot. Since the complexity of stellar winds was not accounted for in the past, any previous mass-loss rate estimate of old stars could be wrong by up to a factor of 10.”

Following this discovery, the team will now research how it impacts other crucial characteristics involved in the life and death stars like the Sun. In the process, the team believes that their research will add more depth to our view of stars.

The Stellar winds around R Hydrae take a more conical shape (L. Decin, ESO/ALMA)

“We were very excited when we explored the first images,” adds co-author Miguel Montargès, also from KU Leuven. “Each star, which was only a number before, became an individual by itself. Now, to us, they have their own identity. “This is the magic of having high-precision observations: stars are no longer just points anymore.”

But, whilst we are on the subject of the future, the team says their findings have particular ramifications for the end of our own star.

Death Spiral: How the Sun Dies and What it Leaves Behind

The Sun is roughly halfway through its lifetime, with half its core hydrogen exhausted, meaning that in approximately 5 billion years it will start to die. For a star of the Sun’s mass, this means undergoing the transformation into a red giant.

For stars with masses greater than the Sun, the collapse of their core will spark a new lease of life, with the fusion of helium into heavier elements being kick-started by tremendous gravitational pressure, providing an outward force that halts the collapse.

The Sun, in contrast, will fade as its core cools, the planetary nebula will continue to expand outwards, ultimately resulting in a white dwarf surrounded by diffuse material that was once its outer layers. 

The team’s research gives us an idea of just what shape this planetary nebula will take, and how it will be crafted by the solar system’s largest planets. “Jupiter or even Saturn — because they have such a big mass — are going to influence whether the Sun spends its last millennia at the heart of a spiral, a butterfly, or any of the other entrancing shapes we see in planetary nebulae today,” Decin notes. 

“Our calculations now indicate that a weak spiral will form in the stellar wind of the old dying Sun.”

Astronomers may have found a twin solar system thousands of light-years away

The newly discovered planet candidate KOI-456.04 and its star Kepler-160 (second panel from above) have great similarities to Earth and sun (top panel). Credit: MPS / René Heller.

In the last 14 years, astronomers have identified more than 4,000 planets orbiting far-away solar systems, but none seems to come close to KOI-467.04. Don’t be fooled by its unceremonious designation, for this is a rare astronomical gem.

According to a new study led by researchers at the Max Planck Institute for Solar System Research in Göttingen, Germany, KOI-467.04 is less than twice the size of Earth and orbits a star that is almost like a twin to our Sun. What’s more, the exoplanet orbits its star at a distance similar to that between Earth and the Sun, suggesting that its surface temperature is conducive to life.

In other words, the scientists may have found a twin solar system — all that astronomers have been wishing for since the first exoplanet was discovered in 1992.

Billions of planets, but there’s only one place like home… or is there?

There are billions — perhaps trillions — of stars in the Milky Way galaxy alone and, on average, each of those stars has at least one planet orbiting them

“We are seeing just how diverse planets are. Planets are more common than they were thought to be before the first exoplanets were found. The number of planets in our galaxy is at least as large as the number of stars. But while planets and planetary systems are so diverse, planets like Earth may be very, very rare,” Dr. Jack Lissauer, a scientist at the NASA Ames Research Center and co-investigator of the Kepler mission, told me last year at a conference in Budapest.

The vast majority of exoplanets identified by astronomers in the past are the size of gas giants like Neptune or Jupiter and orbit their parent stars much too close for life to stand a chance.

Occasionally, astronomers will come across exoplanets that are Earth-sized and potentially rocky, but these planets either orbit too close or too far away from the star. On the extremely rare occasion that scientists discover an Earth-sized rocky exoplanet orbiting in the Goldilocks Zone — or habitable zone, where the distance from the parent star is just right for liquid water to form.

But even then, things are typically far from perfect. Almost all exoplanets less than twice the size of Earth found thus far orbit around a red dwarf, which present their own set of limitations.

Red dwarfs are by far the most common types of stars in the Universe. They’re small, dim, and relatively cool, and also have a long lifetime.

Yet, although life on an exoplanet orbiting a red dwarf would have twice as much time than that on Earth to evolve, it would have to overcome other important challenges.

One has to do with radiation. While the surface temperature might be just right for liquid water to form, exoplanets orbiting red dwarfs are mostly hit by infrared rather than visible light.

If that wasn’t enough, red dwarfs also regularly spew powerful solar flares that can fry nearby planets. What’s more, because red dwarfs are so faint, exoplanets hoping to harbor life need to orbit so close to the parent stars that they get deformed by the stellar gravity. This can result in tidal heating that can trigger global volcanism and turn the promising exoplanet into a hellish world.

So, it’s not just a question of exoplanet quality, stellar quality is vital too. Now, an international team of researchers think they’ve found one that checks all the boxes.

Mirror Earth and Sun

The Earth-like planet candidate that orbits a sun-like star is located over 3,000 light-years away, in the Kepler-170 system.

It was first identified in 2009 and since 2014, astronomers have found that it hosts two exoplanets, known as Kepler-160b and Kepler-160c, which are both much bigger than Earth and in relatively close orbits around their stars. Nothing to warrant particular attention so far.

But then the researchers combed the archival Kepler data of Kepler-160 hoping to perhaps find other planets using a novel method developed by Michael Hippke and René Heller, both from Max Planck. Their investigation was prompted by evidence that Kepler-160c’s orbit was perturbed — something was out there.

This is when they found another two planets, among them the exciting KOI-456.04.

“Our analysis suggests that Kepler-160 is orbited not by two but by a total of four planets,” Heller said in a statement.

 “The planetary signal is so faint that it’s almost entirely hidden in the noise of the data. Our new search mask is slightly better in separating a true exoplanetary signal from the noise in the critical cases,” Heller adds.

According to Heller and colleagues, KOI-456.04 has a radius of 1.9 Earth radii (almost twice as large as Earth) and orbits its parent star every 378 days — that’s mighty close to Earth’s 365 days (or 366 days during a leap year).

As for the star, the astronomers estimate that its radius is 1.1 that of the Sun, with a surface temperature of around 5,200 degrees Celsius, just 300 degrees shy of that of the sun. Its luminosity is also sun-like.

Given this information, the researchers believe that KOI-456.04 might have an average surface temperature of around 5 degrees Celsius, as long as it has an atmosphere that can support at least a mild Earth-like greenhouse gas effect.

“KOI-456.01 is relatively large compared to many other planets that are considered potentially habitable. But it’s the combination of this less-than-double the size of the Earth planet and its solar type host star that make it so special and familiar,” Heller 

Don’t get too excited, though. As a caveat, the researchers claim that they cannot entirely rule out KOI-456.01 as a statistical fluke. According to the study published in the journal Astronomy & Astrophysics, the odds of KOI-456.04 being a real planet and not some statistical aberration is 85%. Formal planetary status requires a 99% degree of confidence.

All hope is not lost, though. Astronomers will have a good chance to confirm their findings once ESA’s PLATO space mission launches in 2026. Plato will specialize in the examination of rocky exoplanets orbiting in habitable zones around Sun-like stars, particularly focusing on the potential for these planets to hold liquid water. Fingers crossed.

NASA planet-hunting satellite finds its first Earth-sized alien world

A picture of TOI 700 with one of the three planets found by TESS (NASA’s Goddard Space Flight Center)

A team of researchers announced on January 6 that NASA’s Transiting Exoplanet Survey Satellite (TESS) discovered its first Earth-sized planet which has the possibility to harbor oceans. The same day, it was also revealed that she had found her first circumbinary planet, a world orbiting two stars.

Coined TOI 700 d (TOI is short for “Tess Object of Interest”), the exoplanet is located 101.5 light-years away and is one of only a few Earth-sized worlds discovered in its star’s habitable zone so far. The discovery was confirmed by NASA’s Spitzer Space Telescope.

TESS monitors large swaths of the sky, called sectors, for 27 days at a time. This long stare allows the satellite to track changes in stellar brightness caused by an orbiting planet crossing in front of its star from our perspective, an event called a transit.

The telescope, which launched in April 2018, hunts for planets using the “transit method,” where it looks for telltale dips in stellar brightness that is caused by orbiting worlds crossing their parent stars’ faces from the satellite’s perspective. This was the same strategy used by NASA’s Kepler space telescope, which discovered about 70 percent of the roughly 4,000 known exoplanets.

“TESS was designed and launched specifically to find Earth-sized planets orbiting nearby stars,” said Paul Hertz, astrophysics division director at NASA Headquarters in Washington. “Planets around nearby stars are easiest to follow-up with larger telescopes in space and on Earth. Discovering TOI 700 d is a key science finding for TESS. Confirming the planet’s size and habitable zone status with Spitzer is another win for Spitzer as it approaches the end of science operations this January.”

TOI 700 d was one of three planets discovered orbiting the star TOI 700. It is the outermost known planet in the system and the only one in the habitable zone. It’s 20 percent larger than Earth, orbits every 37 days and receives from its star 86 percent of the energy that the Sun provides to Earth. The innermost planet discovered, TOI 700 b, is roughly Earth-sized and completes a full orbit every 10 days. The center planet, TOI 700 c, is 2.6 times bigger than Earth, meaning it’s likely a gassy “mini-Neptune,” and circles TOI 700 every 16 days.

TOI 700 is a small, cool M dwarf star located just over 100 light-years away in the southern constellation Dorado. It measures roughly 40 percent of our Sun’s mass and size and has about half its surface temperature. The star appears in 11 of the 13 sectors TESS observed during the mission’s first year, and scientists caught multiple transits by its three planets. It was originally misclassified in the TESS database as being more similar to the Sun, which meant the planets appeared larger and hotter than they really are.

“When we corrected the star’s parameters, the sizes of its planets dropped, and we realized the outermost one was about the size of Earth and in the habitable zone,” said Emily Gilbert, a graduate student at the University of Chicago.

Normally planets which orbit red dwarfs like TOI 700 aren’t a good place to look for life due to powerful flares from the star which will generally fry a planet’s atmosphere. However, TOI 700 d seems to be an exception to this norm. It is also tidally locked, which means that one side is always in daylight.

“In 11 months of data, we saw no flares from the star, which improves the chances TOI 700 d is habitable and makes it easier to model its atmospheric and surface conditions,” said Gilbert.

Because TOI 700 is bright, nearby, and shows no sign of stellar flares, the system is a prime candidate for precise mass measurements by current ground-based observatories. These measurements could confirm scientists’ estimates that the inner and outer planets are rocky and the middle planet is made of gas.

An artist’s depiction of K2-18b orbiting its host star (ESA/Hubble, M. Kornmesser)

This comes on the heels of the detection of water vapor in September 2019 on a potentially habitable planet for the first time. This planet, called K2-18b and discovered by the Kepler telescope, is a super-Earth that orbits a red dwarf star 110 light-years away. K2-18b is the only known exoplanet with water vapor, an atmosphere, and a temperature range that could support liquid water on its surface.

The other first for TESS was the discovery of planet TOI 1338 b which resides in the system TOI 1338, 1,300 light-years away in the constellation Pictor. The two stars there orbit each other every 15 days. One is about 10 percent more massive than the Sun, while the other is cooler, dimmer and only one-third the Sun’s mass.

TOI 1338 b is the only known planet in the system. It’s around 6.9 times larger than Earth, or between the sizes of Neptune and Saturn. The planet orbits in almost exactly the same plane as the stars, so it experiences regular stellar eclipses.

Planets orbiting two stars are usually harder to detect than those orbiting just one. TOI 1338 b’s transits are irregular, between every 93 and 95 days, and vary in depth and duration thanks to the orbital motion of its stars. TESS only sees the transits crossing the larger star; the transits of the smaller star are too faint to detect.

Future missions may be able to identify whether the TESS’s discoveries have atmospheres and, if so, even determine their compositions.

X-Rays could sterilise alien planets that would be otherwise habitable

Intense radiation could peel off the ozone layer around Earth-like planets, essentially wiping out all land life in the process.

A diagram of the Habitable Zone, sometimes called the Goldilocks Area. Shown is temperature vs starlight received. Some notable exoplanets are placed on the diagram, plus Earth, Venus, and Mars. Image credits: Chester Harman.

Astronomers have already discovered over 3,700 planets orbiting stars other than the Sun. Out of them, several are rocky and comparable in size to Earth, and out of these, some are in the so-called Habitable Zone — orbiting their stars in just the right range that allows for liquid water to exist on the surface. But just because they’re in the Habitable Zone that doesn’t necessarily mean they’re habitable.

Most planets we’ve found so far (and presumably, most in our galaxy) orbit red dwarf stars — relatively cool stars, significantly smaller than the sun. In order to be in the habitable zone, planets around red dwarfs need to be closer to their star, which exposes them to X-rays.

Although they’re smaller and cooler, red dwarfs can produce significant X-ray emissions, often during large flares of radiation and eruptions of particles in so-called coronal mass ejections (CMEs). In order to assess the risk of such an ejection, Eike Guenther of the Thueringer Observatory in Germany has been monitoring CMEs from red dwarfs. Just last month, he observed a giant flare from the star AD Leo, located 16 light years away in the constellation of Leo.

AD Leo hosts a known giant planet and potentially many others which we haven’t discovered yet. Guenther’s initial results showed that the giant planet was unaffected, and unlike most flares in our solar system, the radiation flare was not accompanied by a CME. This is good news for life around red dwarfs — around smaller stars, X-ray ejections aren’t that common, so there’s a smaller chance of a devastating X-ray event.

But even so, if such an ejection does take place, it could easily cut through the atmosphere of an Earth-like planet, reaching the surface, and wiping out 94% of the planet’s ozone layer — enough to destroy all land life. Astronomers warn that if there’s an event that could be fatal for most or all life on the planet, a small chance isn’t small enough.

“Astronomers are mounting a global effort to find Earth-like worlds, and to answer the age-old question of whether we are alone in the Universe. With sporadic outbursts of hard X-rays, our work suggests planets around the commonest low-mass stars are not great places for life, at least on dry land,” Guenther concludes.

The study has not yet been peer-reviewed and will be presented at the European Week of Astronomy and Space Science.

The reason why we haven’t found alien life yet might be because we’re searching too soon

An artist’s impression of a planet with two exomoons orbiting in the habitable zone of a red dwarf. Credit: NASA // Wikimedia Commons

In our very own galaxy, there are up to 400 billion stars and around 100 billion planets, out of which an estimated 40 billion Earth-like exoplanets should be orbiting sun-like stars or red dwarfs in a habitable zone. Faced with this sort of numbers for only for one galaxy — our own — many scholars naturally assert that Earth ought not to be the sole life-bearing planet out there. Yet, for better or worse, our giant radio telescopes haven’t picked up any artificial alien signals. Faced with such uncertainties, scientists nowadays are going wild with all sorts of educated assumptions and hypotheses in an effort to unravel this existential dilemma.

A head start

While previous research seems to indicate the chances of Earth being the only place in the galaxy capable of fostering life are slim, one team of astronomers and physicists led by Harvard University’s Avi Loeb are exploring an alternate route. Their research concludes that planets orbiting dim stars called red dwarfs are the best place to look for extraterrestrial life. The catch: life shouldn’t spring in these sort of places for another 10 trillion years. For comparison, the universe is thought to be 13.7 billion years old. That’s a lot of waiting time. It follows, that maybe — just maybe — life on Earth is singular, or among the very first.

Red dwarfs are by far the most common stars in the universe, comprising about three-fourths of all stars based on space telescope observations made so far. Red dwarf stars typically have a mass of between 7.5% and 40% of the Sun, and this lower mass means that red dwarfs have a cooler surface temperature than the Sun, typically around 3,500 Kelvin (3,230 degrees Celsius) compared to over 5,750 Kelvin (5,475 degrees Celsius) for the Sun.

Artist's conception of a red dwarf, the most common type of star in the Sun's stellar neighborhood, and in the universe. Although termed a red dwarf, the surface temperature of this star would give it an orange hue when viewed from close proximity. Credit: Wikimedia Commons

Artist’s conception of a red dwarf, the most common type of star in the Sun’s stellar neighborhood, and in the universe. Although termed a red dwarf, the surface temperature of this star would give it an orange hue when viewed from close proximity. Credit: Wikimedia Commons

A potentially habitable planet — meaning it revolves around a stable orbit and can sustain liquid water and an atmosphere — from a red dwarf system thus has to be a lot closer to the energy source (the red dwarf) than an Earth-like planet around a sun-like star. However, red dwarfs can last for up to 1,000 times longer than sun-like stars because they need far less fuel to sustain the nuclear fusion.

Loeb and colleagues calculated the relative formation probability per unit time of habitable Earth-like planets starting from the first stars and continuing to the distant cosmic future. One core assumption was that habitable planets need to sustain “life as we know it” — carbon-based, water-dependent and within a certain temperature range. Then, assuming life is indeed possible to form around red dwarfs, the researchers found that extraterrestrial life is 1,000 times more likely to arise in the distant future than it is today. A very distant future, as outlined earlier.

“That’s surprising,” says Loeb. “It means that life around the sun is probably a bit early.”
“If it turns out that low-mass stars are able to support life, then we are special because we are one of the early forms of life,” Loeb says.

Whether red dwarfs can host any life whatsoever is still a matter of debate. Because these stars are so dim, potentially habitable planets need to orbit very closely around their red dwarf parents, which might subject them to radiation and solar flares.

The upcoming Transiting Exoplanet Survey Satellite and James Webb Space Telescope could help settle this debate once they become operational and use their spectroscopic instruments to peer into the chemical makeup of plants orbiting red dwarfs. It might take anything from a decade to a couple of decades before this happens, though. Until then, Loeb’s hypothesis is both entertaining and somewhat depressing. No one likes to be the first comer to a party.

Astronomers confirm the existence of potentially habitable super-Earth

Exoplanet GJ581d is the first potentially habitable world astronomers have discovered, but some astronomers believed that the planet wasn’t actually there – it was all an observational flaw mixed with some noise in the signal. However, British researchers recently released a study which confirms that the planet does exist and further underline the matter of habitability. This is one of the planets outside our solar system most likely to harbor life.

Artist’s Impression Of Gliese 581 Planetary System. Image via NSF.

Leading author of the paper, Dr Guillem Anglada-Escudé, said:

“There are always discussions among scientists about the ways we interpret data but I’m confident that GJ 581d has been in orbit around Gliese 581 all along. In any case, the strength of their statement was way too strong. If they way to treat the data had been right, then some planet search projects at several ground-based observatories would need to be significantly revised as they are all aiming to detect even smaller planets. One needs to be more careful with these kind of claims”

The star Gliese 581 is a red dwarf about 20 light years away from Earth in the constellation Libra. Its estimated mass is about a third of that of the Sun and research suggests that three planets orbit it – one being Gliese 581d. The importance of this planet is double fold:

“The existence (or not) of GJ 581d is significant because it was the first Earth-like planet discovered in the ‘Goldilocks’-zone around another star and it is a benchmark case for the Doppler technique.”

The so-called ‘Goldilocks’ area (more technically called the circumstellar habitable zone (CHZ), or simply the habitable zone) is the region around a star within which planetary-mass objects with sufficient atmospheric pressure can support liquid water at their surfaces – in other words, it’s the area around a star in which we would expect to find life (at least life as we know it).

The planet GJ 581d is likely a super-Earth, much like our Earth except much larger, but that doesn’t reduce its chances of hosting life. However, we are still not able to confirm or infirm this – and unfortunately, we won’t be anytime soon. But in time, as astronomers continue to discover more and more potentially habitable planets, the chance of discovering extraterrestrial life seems to grow more and more.

Journal Reference: Paul Robertson, Suvrath Mahadevan, Michael Endl, Arpita Roy. Response to Comment on “Stellar activity masquerading as planets in the habitable zone of the M dwarf Gliese 581”. DOI: 10.1126/science.1260974

star flyby oort cloud

70,000 Years Ago, a Rogue Star Passed Through Our Solar System

Too close for comfort – a team of astronomers from the US, Europe, Chile and South Africa concluded that a dim star passed through the Oort cloud, our solar system’s distant cloud of comets. The star missed the Earth by less than one light year, and passed five times closer than the current closest star, Proxima Centauri.

star flyby oort cloud

Artist’s conception of Scholz’s star and its brown dwarf companion (foreground) during its flyby of the solar system 70,000 years ago. The Sun (left, background) would have appeared as a brilliant star. The pair is now about 20 light years away.
Credit: Michael Osadciw/University of Rochester.

In a paper published in The Astrophysical Journal Letters, lead author Eric Mamajek from the University of Rochester and his team studied the velocity and trajectory of a low-mass star system – WISE 0720-0846 (nicknamed “Scholz’s star”). Due to its low luminosity, the star was discovered only a year ago by astronomer Ralf Dieter-Scholz in Potsdam, Germany, through the use of NASA’s WISE (Wide Field Infrared Survey Explorer), which mapped the entire sky in infrared during the years 2010 and 2011.

Since it was discovered, it had some interesting characteristics. despite being fairly close (“only” 20 light years away), it showed very slow tangential motion, that is, motion across the sky. By studying its trajectory and velocity, astronomers found that the star was either moving towards, or away from our solar system. They reconstructed its past movement and quickly realized it was moving away from our solar system, which means that it passed through it (or very close to it) sometime in the past.

“Most stars this nearby show much larger tangential motion,” says Mamajek, associate professor of physics and astronomy at the University of Rochester. “The small tangential motion and proximity initially indicated that the star was most likely either moving towards a future close encounter with the solar system, or it had ‘recently’ come close to the solar system and was moving away. Sure enough, the radial velocity measurements were consistent with it running away from the Sun’s vicinity — and we realized it must have had a close flyby in the past.”

Scholz’s star moved much faster than expected, and missed Earth by “a whisker” – in astronomical terms, that is. It passed roughly 0.8 light years away from Earth, at 8 trillion kilometers; this happened 70,000 years ago. It may seem like a lot, but it’s really too close for comfort. This fits with an earlier theory, which proposed that such close flybys take place every 100,000 years or so. These encounters could hit the Oort cloud and trigger “comet showers” in the solar system.

“Sure enough, the radial velocity measurements were consistent with it running away from the sun’s vicinity — and we realized it must have had a close flyby in the past,” Mamajek said in a news release.

 

The star is a rogue star – a star that has escaped the gravitational pull of its home galaxy and is moving independently in or towards the intergalactic void; the movement of rogue stars is often hard to predict. A 2012 study claimed that rogue planets riddle the Milky Way, and while rarer, there are also rogue stars in our galaxy.

Currently, Scholz’s star is a small, inconspicuous red dwarf in the constellation of Monoceros, about 20 light years away. The star is part of a binary star system, composed of a low-mass red dwarf star (with mass about 8% that of the Sun) and a “brown dwarf” companion (with mass about 6% that of the Sun). Red dwarfs are by far the most common type of star in the Milky Way, at least in the neighborhood of the Sun, but due to their low luminosity, they are difficult to observe and study. Brown stars are “failed stars” – substellar objects not massive enough to sustain hydrogen-1 fusion reactions in their cores, unlike … well, stars.

Journal Reference:

  1. Eric E. Mamajek, Scott A. Barenfeld, Valentin D. Ivanov, Alexei Y. Kniazev, Petri Väisänen, Yuri Beletsky, Henri M. J. Boffin. THE CLOSEST KNOWN FLYBY OF A STAR TO THE SOLAR SYSTEM. The Astrophysical Journal, 2015; 800 (1): L17 DOI: 10.1088/2041-8205/800/1/L17

 

New Study Suddenly Makes Billions of Exoplanets Habitable

Astronomers hunting for habitable Earth-like planets now believe that the best place to look is not around stars like our Sun, but rather around smaller, cooler stars—orange and red dwarfs. These are by far the most abundant stars in our galaxy, and all of them have at least one exoplanet.

Artist representation of a red dwarf surrounded by 3 planets. Image via Wiki Commons.

Red Dwarfs are smaller and cooler than our Sun, ranging from a mass of of 0.075 solar masses to about 0.50 solar masses. Red dwarfs are by far the most common stars in the Milky Way galaxy and in the entire Universe, but due to their low luminosity they are pretty hard to observe. It’s estimated that some 75 percent of all stars in the universe are red dwarfs, and all of them host planets.

The habitability of red dwarfs has been discussed many times, and is still a matter of debate. Of course, knowing if the most common stars in the universe can host habitable planets is a big deal. Among the problems raised against habitability is the so called tidal locking: just like our planet sees only one side of the moon at all times, so do the red dwarfs; they only see one side of the planet, which means that one side is likely a desertic landscape, while the other is a frozen nightmare.

Above: How heat is distributed on a spinning planet versus a rotationally locked one. Image via Popular Mechanics.

 

This happens when the planet is close to its star, as planets would have to be closer to red dwarfs to be habitable. Naturally, in this case the chances for life are much smaller (though it’s not completely impossible). However, this new study challenges this idea, and claims that not all planets are engaged in tidal locking.

The simple existence of an atmosphere, researchers argue, is enough to ensure that the planet is rotating and revolving around its star, making it much more likely to be habitable. According to Jérémy Leconte, the theoretical astrophysicist at the University of Toronto who lead the study, this means that we may have already discovered many habitable planets – we just don’t know it yet.

“Planets with potential oceans could thus have a climate that is much more similar to the Earth’s than we’ve previously expected,” he says.

So how does the atmosphere play into this problem? Jeff Coughlin, a SETI astronomer working with Kepler planet-hunting mission, who was not involved in the study explains it like this:

“On Earth, light from the sun is what drives the weather in our atmosphere. And that weather, in the form of wind, constantly pushes against the planet—running into mountains, for example, or creating waves on the ocean. This friction is deposited in the rotation rate of our planet, helping to speed it up or slow it down.”

Astrophysicists have known this for quite a while, but according to initial calculations, the atmosphere would have to be incredibly massive to have this impact. We have a good case study very close to us: Venus. Venus’ atmosphere is just big enough to escape lockup, and Venus’ atmosphere is absolutely huge – about 90 times heavier than our own. So scientists discarded the idea.

But when Leconte and his team ran simulations to see how the atmosphere would play into gravitational locking, they surprisingly found that thinner atmospheres actually have a larger rotational effect on their planets. This may seem counterintuitive, but it happens because a thinner atmosphere scatters less sunlight. This creates extra heat which in turn creates a stronger atmospheric tide (a bulging of atmosphere, much like our ocean’s tides). This results in a stronger planetary rotation. If Venus were to have an atmosphere like Earth’s, it would spin 10 times faster.

Armed with the results of this model, the team showed that Earth-sized planets can spin quite healthily around a red dwarf if they have an atmosphere.

“More and more, we’re discovering that there’s a lot of ways to have a very nice, habitable planet around dwarf stars,” Coughlin says. But there’s something more at play here. “We really shouldn’t be so narrow-minded in our assumptions about what types of planets could or could not be habitable,” he says. Coughlin says that even a locked-up rotation is not necessarily a killer for a planet in terms of habitability—strong winds could help smooth out the temperature between the two sides.

It would be nice if we’d be able to confirm this model with some observed information, but until that, the results of this study are pretty convincing.

“Every time we’ve made simple assumptions about habitability,” he says, “we find out new ways why and how they don’t apply.”

Journal Reference: Jérémy Leconte, Hanbo Wu, Kristen Menou, Norman Murray. Asynchronous rotation of Earth-mass planets in the habitable zone of lower-mass stars. Science DOI: 10.1126/science.1258686

All Red Dwarf stars have planets orbiting them

A new study has concluded that virtually all red dwarfs, the stars which make up at least three quarters out of all the stars in the Universe, have planets orbiting them.

The study suggested that habitable-zone super-Earth planets (where liquid water, and therefore life as we know it can exist) orbit around at least a quarter of the red dwarfs in the Sun’s own neighborhood. Among the planets which astronomers described there were also three planets classified as habitable-zone super-Earth.

Artist’s impression. Credit: Neil Cook, University of Hertfordshire.

Dr Mikko Tuomi, from the University of Hertfordshire’s Centre for Astrophysics Research and lead author of the study, said:

“We were looking at the data from UVES alone, and noticed some variability that could not be explained by random noise. By combining those with data from HARPS, we managed to spot this spectacular haul of planet candidates. We are clearly probing a highly abundant population of low-mass planets, and can readily expect to find many more in the near future – even around the very closest stars to the Sun.”

This research is highly important not only for its own discoveries, but also for the promise it holds for the future. Basically, the team figured out a new method that enables new discoveries with existing data. What they did was they measured how much a star “wobbles” in space as it is affected by a planet’s gravity. A planet’s gravity, while extremely small compared to the star, still has a noticeable effect on it. Basically, since planets have no light, researchers detect them based on the wobble of these planets. This periodic wobble is detected in the star’s light.

Professor Hugh Jones, also from the University of Hertfordshire, commented:

“This result is somewhat expected in the sense that studies of distant red dwarfs with the Kepler mission indicate a significant population of small radius planets. So it is pleasing to be able to confirm this result with a sample of stars that are among the brightest in their class.”

This researchers adds another 8 to the 17 previously known planets orbiting red dwarfs – and that number can only go up as time passes on.

Black hole ripping apart a red dwarf that’s orbiting at records speeds

ESA’s XMM-Newton space telescope has found a star and a black hole that orbit each other at the whopping rate of once every 2.4 hours. Basically, the star orbits the black hole at 2,000,000 km/hr.

red dwarf black hole

The black hole here is 3-4 times heavier than the Sun, while the red dwarf has a mass just 20% that of the Sun. Because their masses are comparable, the red dwarf doesn’t truly orbit the black hole, but rather they both orbit their common center of gravity.

“The companion star revolves around the common centre of mass at a dizzying rate, almost 20 times faster than Earth orbits the Sun. You really wouldn’t like to be on such a merry-go-round in this Galactic fair!” says lead author Erik Kuulkers of ESA’s European Space Astronomy Centre in Spain.

His team also saw that they lie high above the Galactic plane, out of the main disc of our spiral Galaxy, an unusual characteristic shared only by two other black-hole binary systems.

Another thing to note is that the centripetal force (the force that makes a body follow a curved path) acting on the red dwarf is much stronger on the side of the red dwarf facing the black hole than the outside. The difference between these two forces is so large that the star is literally being torn apart.

“These high galactic latitude locations and short orbital periods are signatures of a potential new class of binary system, objects that may have been kicked out of the Galactic plane during the explosive formation of the black hole itself,” says Dr Kuulkers.

A A red dwarf is a small and relatively cool star. They are by far the most common type of star in our galaxy, but due to their low luminosity, they are often very hard to spot. Even the largest red dwarfs have just 10% of the Sun’s luminosity.

Via ESA

An artist's impression of an Earth-like planet with two moons orbiting around a red dwarf star. (c) David A. Aguilar (CfA).

Earth-like planets closer than previously thought. Nearest one might lie 13 light-years away

After researchers surveyed data from the Kepler mission tasked with identifying possibly habitable planets outside our solar system they found that 6% of red dwarfs – the most common type of planets – are within this zone. This new adjustment would mean that the nearest Earth-like planet might lie just 13 light years away.

An artist's impression of an Earth-like planet with two moons orbiting around a red dwarf star. (c) David A. Aguilar (CfA).

An artist’s impression of an Earth-like planet with two moons orbiting around a red dwarf star. (c) David A. Aguilar (CfA).

Astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) first took a look at the entire Kepler catalog of 158,000 target stars to identify all the red dwarfs. Then a more refined method was used to assess the stars’ temperature and size, an analysis that showed that these were generally smaller and cooler than previously thought.

An exoplanet is discovered and has its properties determined based on its transient orbit in plane with its parent star. This implies that the exoplanet’s size and properties are the same time determined based on its host star, since they’re based relative to the star’s properties. Thus, cooler dwarf stars means cooler planets and a tighter habitable zone.

“We thought we would have to search vast distances to find an Earth-like planet. Now we realize another Earth is probably in our own backyard, waiting to be spotted,” said Harvard astronomer and lead author Courtney Dressing (CfA).

A new Earth might be closer to us than thought

Red dwarfs make up three out of every four stars in our galaxy for a total of at least 75 billion. The astronomers involved in the present study identified 95 planetary candidates orbiting such red dwarf stars. Upon closer inspection most of them didn’t fit the right size and temperature requirements needed for them to be considered Earth-like, though. Three candidate planets, however, were considered both warm and Earth-sized. This would statistically imply that some 6% of all red dwarfs should have an Earth-like planet orbiting.

“We now know the rate of occurrence of habitable planets around the most common stars in our galaxy,” said co-author David Charbonneau (CfA). “That rate implies that it will be significantly easier to search for life beyond the solar system than we previously thought.”

It so has it that our solar system is located in a cloud of red dwarfs, which is why more than 75% of all neighboring stars are red dwarfs. With this new analysis in play, this all adds up implying that the nearest Earth-like planet might lie just 13 light years away.

Actually locating an Earth-like planet, with all its perks, would require an analysis of its atmosphere, something not possible with today’s technology. Once with the deployment of massive space telescopes like the James Webb Space Telescope or ground based telescope arrays like the Giant Magellan Telescope probing a distant world’s chemistry will be possible – expect some of humanity’s greatest discoveries to be made once this happens.

The three habitable-zone planetary candidates identified in this study are Kepler Object of Interest (KOI) 1422.02, which is 90 percent the size of Earth in a 20-day orbit; KOI 2626.01, 1.4 times the size of Earth in a 38-day orbit; and KOI 854.01, 1.7 times the size of Earth in a 56-day orbit. All three are located about 300 to 600 light-years away and orbit stars with temperatures between 5,700 and 5,900 degrees Fahrenheit. (For comparison, our Sun’s surface is 10,000 degrees F.)

Dressing presented her findings today in a press conference at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

source: press release

The great blue marble. Does is it have a sister planet? A question astronomers seek to answer.

How many Earth-like planets are there in the Milky Way? Billions, according to astronomers

One of the most outstanding dreams astronomers and other scientists hope to accomplish is to someday encounter proof that extraterestrial life exists. Intelligent life might be extremely far off, however microbiological life should without a doubt be present elsewhere other than our planet or solar system. For life to blossom, however, the right conditions have to be met, and one of the major prerequisites for life supporting conditions is liquid water. Along the years, scientists have come up with what’s called the habitable zone, an area around a star’s orbit where favorable conditions for harboring life may exist. Now, after hundreds of potential Earth-life planets have been found, scientists have enough data at their disposal to elaborate a statistical hypothesis – there are billions of planets similar to Earth that might potentially support life in our galaxy alone!

The great blue marble. Does is it have a sister planet? A question astronomers seek to answer.

The great blue marble. Does is it have a sister planet? A question astronomers seek to answer.

Astronomers using the European Southern Observatory’s HARPS, a high precision instrument fitted to the 3.6m telescope at the Silla Observatory in Chile, studied 102 red dwarf stars neighbouring the sun over a period of six years. Red dwarfs are smaller and cooler than the sun, however it’s been found that 40% of red dwarf stars may have Earth-sized planets orbiting them that have the right conditions for life.

“Our new observations with Harps mean that about 40% of all red dwarf stars have a super-Earth orbiting in the habitable zone where liquid water can exist on the surface of the planet,” said team leader Xavier Bonfils from the Observatoire des Sciences de l’Univers de Grenoble, France.

“Because red dwarfs are so common – there are about 160 billion of them in the Milky Way – this leads us to the astonishing result that there are tens of billions of these planets in our galaxy alone.”

During their survey, the group of astronomers found a total of nine super-Earths, planets with a rocky structure that have a mass up to ten times that of Earth, while two such planets are orbiting inside their stars’ habitable zones. Extrapolating with data gathered from non-dwarf stars were super-Earths have also been found, the scientists were able to produce an estimate for how common different sorts of planets are around red dwarf.

Huge planets, the size of Jupiter for instance, have been found to orbit in less than 12% of red dwarfs, suggesting their much rarer than small rocky words, like the Earth. Alright, but why should we care if there’s another potential Earth out there if its thousands of light years away? Well, the scientists found that there could be at least 100 super-Earths’ orbiting in the habitable zones of their stars, located in a radius 30 light years away from our own sun. That’s not that far at all, in the astronomical scale.

The group’s findings were reported in the journal Astronomy and Astrophysics.

[image source]

Physicists create a supernova in a jar

A supernova is a stellar explosion of cosmic proportions, that often can outshine the entire galaxy it is located in, before fading away in a matter of weeks or months. During this short period however, supernovae emit as much energy as the Sun emits during its entire life span – it’s the same kind of phenomena that researchers from the university of Toronto and Rutgers managed to mimic at scale.

In a certain (quite common) type of supernova the detonation starts with a flame ball that is buried deep in a white dwarf; the flame ball is much hotter and brighter than the environment surrounding it, so it rises rapidly making a plume topped with an accelerating smoke ring.

The autocatalytic reactions mainly do two things: they release heat and change the chemical composition of the liquid, which causes some forces that stir it, further progressively amplifying the effects.

“A supernova is a dramatic example of this kind of self-sustaining explosion in which gravity and buoyancy forces are important effects. We wanted to see what the liquid motion would look like in such a self-stirred chemical reaction,” says Michael Rogers, who led the experiment as part of his PhD research, under the supervision of Morris.

“It is extremely difficult to observe the inside of a real exploding star light years away so this experiment is an important window into the complex fluid motions that accompany such an event,” Morris explains. “The study of such explosions in stars is crucial to understanding the size and evolution of the universe.”

“We created a smaller version of this process by triggering a special chemical reaction in a closed container that generates similar plumes and vortex rings,” says Stephen Morris, a University of Toronto physics professor.