Tag Archives: Einstein ring

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].

Hubble snaps amazing photo of Einstein Ring phenomenon

The new picture snapped by the Hubble Telescope and analyzed by NASA scientists is jam-packed with galaxies — and among them, there’s an even more spectacular feature: a so-called Einstein Ring.

Image credits: ESA/Hubble & NASA / Judy Schmidt.

This charming part of the universe is called SDSS J0146-0929, a galaxy cluster which features a great variety of spiral and elliptical galaxies presented to us at different angles — some are face-on, some are angled, but all are locked together by the inescapable tug of gravity. But here, gravity does even more than just hold the galaxies together: it bends light in a way that creates a ring-like feature, a so-called Einstein Ring.

Einstein’s ring occurs when light coming from a bright source is bent by the gravitational effect of a very large structure or object — in this case, SDSS J0146-0929. The phenomenon is called gravitational lensing and requires that the three participants (the light source, the massive structure, and the observer — which is Earth) be aligned in a straight-line configuration of called a syzygy.

In this sense, an Einstein Ring is a special case of gravitational lensing, caused by the exact alignment of the source, lens, and observer. This results in a symmetry around the lens, causing a ring-like structure. NASA’s Karl Hille describes the image:

“In this image, the light from a background galaxy is diverted and distorted around the massive intervening cluster and forced to travel along many different light paths toward Earth, making it seem as though the galaxy is in several places at once.”

Einstein predicted this phenomenon back in 1912, even before his theory of general relativity. However, Einstein didn’t think we’d ever be able to observe one because our technology wasn’t capable of it. Well, our technology has progressed way beyond what Einstein thought possible and today, hundreds of gravitational lenses are currently known. In recent years, astronomers have used gravitational lensing to zoom in on extremely distant parts of the universe.

Just a few days ago, scientists published a study in which they described the farthest start ever observed, and in late 2017, a different team found a planet so big that it might not be a planet after all.

If you think this is awesome (and it is), I’ve got something even more amazing: a few years ago, Hubble snapped a spectacular image of a double Einstein’s ring — an extremely unlikely scenario which astronomers were lucky to witness.

double-einstein-ring

Extremely rare double Einstein ring imaged by Hubble

double-einstein-ring

(c) NASA/ESA

Hubble just never ceases to surprise. The latest astronomical find discovered using the ever resourceful space telescope is a never before encountered double ring pattern known as an Einstein ring. This very rare pattern is the result of a peculiar optical alignment in which three galaxies are perfectly aligned with each other, like beads on a string. The occurrence isn’t just a silly optical trick in space – studying it, astronomers can learn more about dark matter and dark energy, and even the curvature of the Universe.

The phenomenon that gave rise to this peculiar observation is known as gravitational lensing, in which the light emitted by a galaxy in the background gets bent by the gravitational pull of a massive galaxy in the foreground. In our case, one could say we have a double gravitational lens on our hands since a third massive galaxy lies in the foreground. When two galaxies are exactly lined up, the light gets twisted in such a fashion that it forms a shape that resembles a circle, called Einstein’s ring. When three of them are perfectly lined up, such as the case, two concentric rings form.

“Such stunning cosmic coincidences reveal so much about nature. Dark matter is not hidden to lensing,” added Leonidas Moustakas of the Jet Propulsion Laboratory in Pasadena, California, USA. “The elegance of this lens is trumped only by the secrets of nature that it reveals.

The odds of such a phenomenon being observable from Earth’s vantage point are so dim, that the discovery can be considered nothing short of jackpot! In fact, the team of astronomers led by Raphael Gavazzi and Tommaso Treu of the University of California, Santa Barbara were extremely lucky to spot it in the first place. SLACS team member Adam Bolton of the University of Hawaii’s Institute for Astronomy in Honolulu first identified the lens in the Sloan Digital Sky Survey (SDSS). “The original signature that led us to this discovery was a mere 500 photons (particles of light) hidden among 500,000 other photons in the SDSS spectrum of the foreground galaxy,” commented Bolton.

The geometry of the two rings allowed the researchers to establish the mass of the middle galaxy precisely to be a value of 1 billion solar masses – a dwarf galaxy. This is actually the first time a dwarf galaxy’s mass was measured at cosmological distance. The comparative radius of the rings could also be used to provide an independent measure of the curvature of space by gravity.

The results were reported at the 211th meeting of the American Astronomical Society in Austin, Texas, USA. A paper has been submitted to The Astrophysical Journal.

[source]