Tag Archives: ancient galaxy

Using ALMA astronomers have revealed an extremely distant galaxy that looks surprisingly like our Milky Way. The galaxy, SPT0418-47, is gravitationally lensed by a nearby galaxy, appearing in the sky as a near-perfect ring of light. (ALMA (ESO/NAOJ/NRAO), Rizzo et al.)

Distant ‘Milky Way Look-Alike’ Challenges Theories of Galaxy Formation

Using the phenomenon of gravitational lensing astronomers have examined an extremely distant galaxy that shares many features with the Milky Way. The discovery of a calm galaxy so early in the Universe’s history calls into question our theories of how galaxies form. 

Using ALMA astronomers have revealed an extremely distant galaxy that looks surprisingly like our Milky Way. The galaxy, SPT0418-47, is gravitationally lensed by a nearby galaxy, appearing in the sky as a near-perfect ring of light. (ALMA (ESO/NAOJ/NRAO), Rizzo et al.)
Astronomers using ALMA, in which the ESO is a partner, have revealed an extremely distant galaxy that looks surprisingly like our Milky Way. The galaxy, SPT0418-47, is gravitationally lensed by a nearby galaxy, appearing in the sky as a near-perfect ring of light.
(ALMA (ESO/NAOJ/NRAO), Rizzo et al.)

Astronomers have discovered that a distant young galaxy that existed in the very early universe shares some surprising similarities with our galaxy. The fact that the young galaxy named SPT-S J041839–4751.9 or SPT0418–47 for short — located 12 billion light-years from Earth — resembles the Milky Way and the galaxies that surround it presents something of a problem. Galaxies that existed 1.4 billion years after the Big Bang, weren’t supposed to be so calm, unchaotic, and well-formed.

Thus the discovery of this throws many of our theories of galactic evolution into question. In fact, this finding fits into a series of recent discoveries that suggest galaxies began forming much earlier in the Universe’s history than previously believed. 

The research team reconstructed the distant galaxy’s true shape, shown here, and the motion of its gas from the ALMA data using a new computer modelling technique. 
(ALMA (ESO/NAOJ/NRAO), Rizzo et al.)

“This result represents a breakthrough in the field of galaxy formation, showing that the structures that we observe in nearby spiral galaxies and in our Milky Way were already in place 12 billion years ago,” says Francesca Rizzo, a PhD student from the Max Planck Institute for Astrophysics in Germany, and the lead author of a paper detailing the findings published today in the journal Nature

Whilst the observation of this distant galaxy would not have been possible without the impressive technology of the ESO’s Atacama Large Millimeter/submillimeter Array (ALMA) located in the Chilean Andes, it also hinged on the invention of another galaxy, and an extraordinary feature of Einstein’s theory of general relativity. The team reconstructed the accurate image of SPT0418–47 from the ring-like image received by ALMA as a result of gravitational lensing by an intervening galaxy. 

“We have studied in great detail a very distant galaxy. This means going back in time and we see this galaxy when it was very young, 1.4 billion years after the Big Bang,” Rizzo’s co-author, Filippo Fraternali, from the Kapteyn Astronomical Institute, the University of Groningen, Netherlands, tells ZME Science referring to the fact that the light from SPT0418–47 has travelled 12 billion years to reach us.

“Given that galaxies cannot form right after the Big Bang, we can estimate that SPT0418–47 [as we see it] is about 1-billion-years old.”

A Distant Milky Way Doppelganger With Some Key Differences

SPT0418–47 possesses a central bulge and a rotating disc, two features also displayed by the Milky Way and other local galaxies. However, it lacks the Milky Way’s spiral arms and is also much smaller than our home galaxy. This is the first time that astronomers have spotted a central bulge — stars tightly clustered around the galactic centre — in such a distant, and therefore early, galaxy. 

However, Fraternali notes that just because SPT0418–47 resembles the Milky Way at the stage we see it at, that doesn’t mean it evolved just as our galaxy did. “It is important to remark that whilst SPT0418–47 is similar to the Milky Way now, it does not mean that 12 billion years ago the Milky Way looked like SPT0418–47,” the researcher adds.

“In fact, we think that SPT0418–47 will evolve into a galaxy very different from the Milky Way, an elliptical galaxy, much more massive and without gas.”

How Astronomers Reconstructed SPT0418-47 (ALMA (NRAO/ESO/NAOJ)/Martin Kornmesser (ESO)/ Robert Lea)
How Astronomers Reconstructed SPT0418-47 (ALMA (NRAO/ESO/NAOJ)/Martin Kornmesser (ESO)/ Robert Lea)

Another key difference between the two galaxies is that SPT0418–47 is forming stars much more rapidly, unusual for a rotating disk. “SPT-S J041839–4751.9 belongs to a particular population of galaxies that are known as dusty star-forming galaxies,” Simona Vegetti, another co-author on the paper and an expert in gravitational lensing from the Max Planck Institute for Astrophysics, tells ZME Science. “As the name suggests, these are galaxies that are undergoing a significant burst of high-rate star formation.”

Vegetti goes on to explain that astronomers believe that as they age, galaxies like SPT0418-47 will turn into what is referred to as early-type galaxies — a galaxy which has consumed most of its gas and is not forming stars anymore.

“By comparing the properties of SPT-S J041839–4751.9 with those of nearby early-type galaxies, we can learn something about the processes which are responsible for the transformation from one galaxy type to the other,” shes says. “It’s a bit like comparing the properties of young and old people, it gives us some hints on the ageing process.”

But the most puzzling aspect of the distant galaxy is how calm and ordered it appears. Something current cosmological models cannot account for. 

Young and Chaotic? 

Our current cosmological models suggest that the Universe that SPT0418–47 as we see it inhabited was a chaotic and turbulent place. And galaxies found during this epoch are expected to reflect these qualities, even if they do possess some structure, this should be washed out by the violent conditions around them. 

“The general idea was that galaxies at those distances/times were extremely chaotic and one would barely recognise a disc in formation in amongst massive filaments of infalling gas and powerful explosions due to the extremely intense star formation,” says Fraternali. 

Galaxies in the early universe are expected to be the site of powerful phenomena like supernova explosions which release a lot of energy Vegetti explains, adding: “We would expect SPT-S J041839–4751.9 to be very turbulent, or in other words, we expect the motion of gas in this galaxy to move chaotically in winds and outflows.”

But the team’s observations reveal a completely different picture. What they actually found was that the motion of the gas in SPT0418–47 is, in fact, rotating around the centre of the galaxy quietly and in a well-ordered fashion. As Vegetti notes: “It is very hard to explain this behaviour within the context of the latest state-of-the-art numerical simulations of galaxies.”

ALMA (ESO/NAOJ/NRAO), Rizzo et al.

One of the man questions that remain for Fraternali is how common are these features and the relatively ‘calmness’ of SPT0418–47 in other older galaxies? “Because the galaxy has not been selected by us — it was, by chance, perfectly aligned with the lens along the line of sight — we may argue that it could be representative of a large fraction of massive galaxies at that time.”

Thus, staring back in time to conduct further investigation of these distant stars is of vital importance. But, that, as you may imagine, is no easy task. In fact, the study of SPT0418–47, as Fraternali indicates, was only made possible by the intervention of another galaxy coming between it and us, and the ensuing remarkable phenomena of gravitational lensing. 

Galaxies as Lenses — the Power of Gravitational Lensing

The exact alignment of SPT0418–47 and an intervening galaxy means that it appears as a near-perfect ring to the team at ALMA — a structure referred to by astronomers as an ‘Einstein ring’ by astronomers due to its connection to the theory of general relativity — the geometrical theory of gravity put forward by Einstein in the early years of the 20th Century. 

Gravitational lensing hinges on the fact that objects with mass curve the fabric of spacetime around them. The greater the mass, the more extreme the curvature. The most common analogy used to describe this is a stretched rubber-sheet having objects of increasing mass placed on it. A bowling ball creating a greater ‘dent’ on the sheet than a marble or a tennis ball. 

This means that an object like a galaxy with tremendous mass curves the path of light travelling past it, often this results in an object behind the lens appearing to be located in a different place. In extreme cases, creating an ‘Einstein Ring’ built up of light that took different curved paths around the intervening galaxy and thus arrived at Earth at slightly different times. But, isn’t just a beautiful and curious phenomenon of gravity, it’s also a powerful observational tool.  

ight from a distant galaxy is distorted by the gravitational effects of a foreground galaxy, which acts like a lens and makes the distant source appear distorted, but magnified, forming characteristic rings of light, known as Einstein rings. This effect has allowed astronomers to see the distant galaxy SPT0418-47 (which appears as a golden ring in the ALMA images) in finer detail than would have been possible otherwise. The foreground galaxy is not visible in the ALMA images of SPT0418-47 because it is too faint at the wavelengths used. The blue colour used in this schematic to represent this foreground galaxy is artificial. Credit: ALMA (NRAO/ESO/NAOJ)/Luis Calçada (ESO)
Light from a distant galaxy is distorted by the gravitational effects of a foreground galaxy, which acts like a lens and makes the distant source appear distorted, but magnified, forming characteristic rings of light, known as Einstein rings. This effect has allowed astronomers to see the distant galaxy SPT0418-47 (which appears as a golden ring in the ALMA images) in finer detail than would have been possible otherwise. The foreground galaxy is not visible in the ALMA images of SPT0418-47 because it is too faint at the wavelengths used. The blue colour used in this schematic to represent this foreground galaxy is artificial. Credit: ALMA (NRAO/ESO/NAOJ)/Luis Calçada (ESO)

“Because these galaxies are very far, it is challenging to study them in great detail using current telescopes, they are not powerful enough,” Vegetti says. “Our team then uses the effect of strong gravitational lensing to overcome this limitation.”

The process used by the team first involves the search for a pair of galaxies that are far away from each other but appear aligned from our vantage point here on Earth. “The galaxy closer to us will then behave like a lens providing us with a magnified view of the more distant galaxy,” Vegetti elaborates. “It’s like observing through a much more powerful telescope. 

“When we started studying this object we had no idea of what we were going to find. There are almost no other studies of galaxies so young at such a level of detail.”

Vegetti explains that the next generation of telescopes such as the James Webb Space Telescope and the ESO’s Extremely Large Telescope (ELT) should allow for the study of SPT0418–47 galactic contemporaries in much greater detail. This will allow researchers to discover just how common these features are, and in turn, possibly spark a rethink of how early well-ordered galaxies could form in the Universe’s history. She also reserves special praise for this study’s lead author.

“These new facilities will bring this type of analysis to the next level, allowing us to observe even younger galaxies with an even greater level of detail,” Vegetti concludes. “Francesca Rizzo is leading the way in this line of research. She is a brilliant young scientist with whom I enjoy working, so I am looking forward to our next discovery!”

Source

Rizzo. F., Vegetti. S., Powell. D., Fraternali. F., et al, ‘A dynamically cold disk galaxy in the early Universe,’ Nature, [2020].

Some ancient Globular Clusters may not be ancient at all

Young globular clusters (ages up to 1 billion years) are indicated by the blue dots. These globular clusters are closely associated with a filamentary network of cool gas, coloured orange to white, which extends to the outer reaches of the giant galaxy at the centre of the Perseus galaxy cluster. Round or oval objects, also coloured orange to white, are smaller galaxies that are part of the same galaxy cluster. (@The University of Hong Kong)

Astronomers believe that globular clusters — found around giant galaxies in the centre of galactic clusters — are ancient relics remaining from the earliest formative stages of galaxies. But, despite this well-founded belief, the physical origins of these clusters — most common around elliptical galaxies — remains something of a mystery. 

New research conducted by Dr Jeremy Lim and his Research Assistant, Miss Emily Wong, at the Department of Physics of The University of Hong Kong (HKU) have used data collected by the Hubble Space Telescope in order to find a surprising answer to this cosmic conundrum. 

Dr Lim’s team discovered that globular clusters around the giant galaxy at the centre of the Perseus galaxy cluster are not all ancient objects. Whilst most globular clusters are believed by scientists to have formed shortly after the Universe began 13.8 billion years ago, a few thousand of the clusters studied by the team seem to have formed over at least the past 1 billion years. Even more, could have possibly formed later in cosmic history the research suggests.

These younger globular clusters seem to be associated with a complex filamentary network of cool gas which extends to the outer reaches of this giant galaxy. This seems to suggest that these clusters were born in this same network. This is significant as this cool gas is thought to have been deposited by the hot gas that infuses the entire Perseus galaxy cluster. The density of this hot gas and thus the rate at which it cools rises in the direction of the galactic cluster’s centre. 

After formation, the newly born galactic clusters are no longer bound to the network of cool gas and begin to fall inwards onto the giant galaxies. This can be considered almost analogous to raindrops condensing in clouds and falling to the ground. 

Old globular clusters (ages up to 10 billion years or more) are indicated by the red dots. These globular clusters are randomly distributed around the giant galaxy at the centre of the Perseus galaxy cluster; this galaxy is the large grey to white oval at the centre of the picture. Round or oval objects, also coloured grey to white, are smaller galaxies that are part of the same galaxy cluster. ( @The University of Hong Kong)

This inward gathering of younger globular clusters after formation in a network of cool gas is in stark contrast to the formation and dispersion of more ancient globular clusters. 

These older clusters form from gas compressed in the spiral arms of galaxies or from dense gas at the centre of galaxy clusters. After their formation, the random dispersion of older clusters across the giant galaxy is a result of them scattering off each other during the course of their orbit around this galaxy. 

Solving lingering puzzles regarding globular clusters

Globular clusters can contain anywhere from hundreds of thousands to several million stars — all of which are born at the same time. These stars are packed incredibly densely, with the clusters having spherical volumes thousands of times smaller than the diameter of our galaxy — the milky way. 

One puzzling aspect of these clusters has been the sheer numbers at which they exist — and how they could have formed at the same point in cosmic history. By showing that some of these clusters form later than others and fall into place — this new research may have solved that puzzle.

Another puzzling aspect of these global clusters is the broad range of colours they display around giant galaxies. Again, this could be a result of the clusters have different respective ages. Globular clusters likely change from blue to red as they age. This is a result of more massive stars burning through their fuel more quickly as nucleosynthesis progresses more quickly in larger stars. As these stars are bluer than smaller stars, as they die it leaves the cluster to take a redder hue. Thus, a broad range of ages would result in a broad range of colours — which is indeed what astronomers observe. 

The team’s research does indicate that despite forming at different times, both older and younger globular clusters in the Perseus galaxy share a common formation mechanism. Irrespective of age, the globular clusters span a broad range of masses — with fewer at the larger mass end of the spectrum. This similar mass trend suggests a common formation mechanism for star clusters across the mass scale regardless of the environment in which they formed. 

This sustained formation of globular clusters over a long range of time could also explain the enormous size of giant galaxies — which can be in excess of ten times that of the Milky Way. As more massive globular clusters within these galaxies endure, their more diminutive counterparts could be ripped apart during their orbits. This leaves the stars which form these smaller globular clusters to be spread through the giant galaxies contributing to their growth in size. 


Original research: ‘Sustained Formation of Progenitor Globular Clusters in a Giant Elliptical Galaxy’ by Jeremy Lim, Emily Wong, Youichi Ohyama, Tom Broadhurst & Elinor Medezinski in Nature Astronomy. 

Ancient Galaxies Really Sucked (Gas, That Is)

When early galaxies formed, there was a surprisingly high rate of new stars being formed, which was explained by major galactic collisions; however, recent evidence suggests that in fact the answer is much simpler, and not nearly as violent.

An artist's representation of a galaxy sucking surrounding gas. Credit: ESO/L. Calçada

Astronomers using the European Southern Observatory’s Very Large Telescope in Chile have observed three ancient galaxies with “patches of star formation” towards their center; they found that these galaxies were literally sucking hydrogen and helium from the space between galaxies and using it as fuel.

“It solves the problem of providing to the galaxies fuel to form their stars in a continuous way, without having to invoke violent mergers and galaxy interactions,” said study researcher Giovanni Cresci of Italy’s OsservatorioAstrofisico di Arcetri. “Those certainly exist, but these new findings show that they are not the main driver of star formation in the early universe.”

Theoretical models developed so far suggest that the earliest galaxies formed about a billion years after the Big Bang, but they were quite small, way smaller than the Milky Way, for example. But somehow they grew in stars and accumulated more and more stars, and so galactic collisions seemed to be a reasonable explanation.

However, recent evidence suggests that such a violent star formation would fade within a few million years, and the studied galaxies showed stars that lasted billions of years. Also, some galaxies showed absolutely no sign of such a collision, so a new solution had to be found.

Cresci and his colleagues concluded that early galaxies have sucked the hydrogen and helium that surrounded them and thus drove new star formation for billions of years. Their study of non-merging galaxies seems to back up their claim.

“This is the link between the large-scale structures dominated by dark matter and the local Hubble-type galaxies such as our own,” he said. “We are trying to understand how our home in the universe, the Milky Way, was built.”

Via Space.com