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Hubble Shows the True Size of Andromeda – Universe Today

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It’s possible that you’ve seen the Andromeda galaxy (M31) without even realizing it. The massive spiral galaxy appears as a grey, spindle-shaped blob in the night sky, visible with the naked eye in the right conditions. It’s the nearest major galaxy to ours, and astronomers have studied it a lot.

Now astronomers have used the Hubble Space Telescope to map out Andromeda’s enormous halo of hot gas.

Scientists call the halo of gas surrounding galaxies the circumgalactic medium (CGM.) The CGM is diffuse, and nearly invisible. But as scientists get the technology to study it more closely, they’re starting to understand the important role it plays in galactic evolution. They think that the CGM is an important source of star-forming material, and that it regulates a galaxy’s gas supply.

“It’s full of clues regarding the past and future evolution of the galaxy, and we’re finally able to study it in great detail in our closest galactic neighbor.”

co-investigator Samantha Berek of Yale University in New Haven, Connecticut.

In a new study, a team of researchers used the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST) to map out Andromeda’s CGM. The title of the study is “Project AMIGA: The Circumgalactic Medium of Andromeda.” The lead author is Nicolas Lehner from the University of Notre Dame in Indiana. The study is published in The Astrophysical Journal.

The study shows that Andromeda’s halo is by far the largest object in the night sky, we just can’t see it. It extends 1.3 million light years from the center of Andromeda, which is about halfway to our galaxy. In some directions, it extends even further, up to 2 million light years. And Andromeda’s halo is actually bumping into the Milky Way’s halo.

At a distance of 2.5 million light-years, the majestic spiral Andromeda galaxy it is so close to us that it appears as a cigar-shaped smudge of light high in the autumn sky. If its gaseous halo could be seen with the naked eye, it would be about three times the width of the Big Dipper—easily the biggest feature on the nighttime sky. Image Credit: NASAESA, J. DePasquale and E. Wheatley (STScI) and Z. Levay

There’s also much more detail in the CGM than researchers thought. There are two layered parts to it: an inner shell of gas is nested inside an outer shell. The inner shell is more dynamic, and the outer shell is hotter and smoother. The team of researchers thinks that the inner shell is more dynamic and turbulent because of outflows from supernovae.

“We find the inner shell that extends to about a half million light-years is far more complex and dynamic,” explained study leader Nicolas Lehner of the University of Notre Dame in Indiana. “The outer shell is smoother and hotter. This difference is a likely result from the impact of supernova activity in the galaxy’s disk more directly affecting the inner halo,” Lehner said in a press release.

It’s not just the dynamic state of the inner halo that points to supernovae. It’s also the composition of the gas itself. The team discovered a lot of heavier elements in the gas, which are created in the hearts of massive stars, and are spread out into space by exploding supernovae.

The gas in the CGM emits some energy on its own, but it’s extremely difficult to see. The researchers studied it by watching the ultraviolet light from distant quasars as it passes through the halo. That ultraviolet light is absorbed by Earth’s atmosphere, so it can’t be observed from the ground. But the Hubble can see it from its position in Low-Earth Orbit (LEO.)

The team found 43 quasars that are “behind” Andromeda from our point of view. Since they’re scattered across the breadth and width of the galaxy, the researchers were able to study the halo in multiple locations. They observed how the ultraviolet light from the distant quasars was absorbed differently in different regions of the CGM. The team used Hubble’s COS to detect ionized gas from carbon, silicon and oxygen.

This illustration shows the location of the 43 quasars scientists used to probe Andromeda’s gaseous halo. These quasars—the very distant, brilliant cores of active galaxies powered by black holes—are scattered far behind the halo, allowing scientists to probe multiple regions. Looking through the immense halo at the quasars’ light, the team observed how this light is absorbed by the halo and how that absorption changes in different regions. By tracing the absorption of light coming from the background quasars, scientists are able to probe the halo’s material. Image Credit: NASA, ESA, and E. Wheatley (STScI)

This isn’t the first time that lead researcher Lehner has studied Andromeda by observing the light from distant quasars. In 2015 he and his colleagues published a pilot study of Andromeda based on the light from only six quasars. That study showed how large and massive Andromeda’s CGM is, but it didn’t reveal all of the complexity. That work was called “Evidence for a Massive, Extended Circumgalactic Medium Around the Andromeda Galaxy” and was also published in The Astrophysical Journal.

“Previously, there was very little information—only six quasars—within 1 million light-years of the galaxy. This new program provides much more information on this inner region of Andromeda’s halo,” explained co-investigator J. Christopher Howk, of Notre Dame. “Probing gas within this radius is important, as it represents something of a gravitational sphere of influence for Andromeda.”

The team also measured the velocity of the gas in the inner and outer haloes. That’s how they determined that the inner shell is more dynamic than the outer shell. The inner shell shows multiple velocity components, while the outer shell shows only one velocity component. The velocity measurements also allowed them to determine that the outer halo is gravitationally bound to Andromeda.

“This is groundbreaking for capturing the complexity of a galaxy halo beyond our own Milky Way.”

Study Leader Nicolas Lehner of the University of Notre Dame in Indiana.

“Understanding the huge halos of gas surrounding galaxies is immensely important,” explained co-investigator Samantha Berek of Yale University in New Haven, Connecticut. “This reservoir of gas contains fuel for future star formation within the galaxy, as well as outflows from events such as supernovae. It’s full of clues regarding the past and future evolution of the galaxy, and we’re finally able to study it in great detail in our closest galactic neighbor.”

Andromeda is really our only opportunity to study a CGM in such detail. Our position inside the Milky Way makes it impossible to study the Milky Way’s own CGM. And no other large galaxy is close enough for our current technology to study in this way. Distant galaxies appear so small that there aren’t enough background quasars for spectroscopy. Each quasar behind a galaxy provides a sight line for scientists.

This image from the study shows the location of distant quasars and their sightlines through Andromeda's CGM. The label calls them QSOs or quasi-stellar objects. Open red circles are the 25 quasar sightlines acquired previously, and filled circles are the 18 acquired for the first time in this study. The grey plus signs are neutral hydrogen observations made with the Green Bank Telescope. Image Credit: Lehner et al, 2020.
This image from the study shows the location of distant quasars and their sightlines through Andromeda’s CGM. The label calls them QSOs or quasi-stellar objects. Open red circles are the 25 quasar sightlines acquired previously, and filled circles are the 18 acquired for the first time in this study. The grey plus signs are neutral hydrogen observations made with the Green Bank Telescope. Image Credit: Lehner et al, 2020.

“This is truly a unique experiment because only with Andromeda do we have information on its halo along not only one or two sightlines, but over 40,” explained Lehner. “This is groundbreaking for capturing the complexity of a galaxy halo beyond our own Milky Way.”

Even though we can’t study the Milky Way’s CGM directly, the researchers say that they can infer certain properties of it based on this study. In their study they write “it is likely that the MW has similarly a cool and warm–hot ionized CGM,” and that the Milky Way’s and Andromeda’s CGM “must most likely already overlap and interact with each other.”

The Hubble Space Telescope has a 2.4 m mirror and the James Webb Space Telescope has a 6.5m mirror. LUVOIR will dwarf them both with a massive 15m mirror. Image: NASA
The Hubble Space Telescope has a 2.4 m mirror and the James Webb Space Telescope has a 6.5m mirror. LUVOIR will dwarf them both with a massive 15m mirror. Image: NASA

As it stands right now, Andromeda is the only galaxy that can be scrutinized in this way. But in the future, that will change. Future UV space telescopes like LUVOIR (Large UV/Optical/IR Surveyor), with its enormous 15m mirror, should allow scientists to study the CGMs of galaxies outside our Local Group. In that sense, this study is giving us a glimpse of some potential future results.

“So Project AMIGA has also given us a glimpse of the future,” said Lehner.

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Salty ponds found on Mars suggest stronger prospect of life on red planet, scientists say – CBC.ca

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A network of salty ponds may be gurgling beneath the South Pole on Mars, alongside a large underground lake, raising the prospect of tiny, swimming Martian life.

Italian scientists reported their findings Monday, two years after identifying what they believed to be a large buried lake. They widened their coverage area by a couple hundred miles, using even more data from a radar sounder on the European Space Agency’s Mars Express orbiter.

In the latest study appearing in the journal Nature Astronomy, the scientists provide further evidence of this salty underground lake, estimated to be 20 to 30 kilometres across and buried 1.5 kilometres beneath the icy surface.

Even more tantalizing, they’ve also identified three smaller bodies of water surrounding the lake. These ponds appear to be of various sizes and are separate from the main lake.

Roughly four billion years ago, Mars was warm and wet, like Earth. But the red planet eventually morphed into the barren, dry world it is today.

The research team led by Roma Tre University’s Sebastian Emanuel Lauro used a method similar to those used on Earth to detect buried lakes in the Antarctic and Canadian Arctic. They based their findings on more than 100 radar observations by Mars Express from 2010 to 2019; the spacecraft was launched in 2003.

All this potential water raises the possibility of microbial life on — or inside — Mars. High concentrations of salt are likely keeping the water from freezing at this frigid location, the scientists noted. The surface temperature at the South Pole is an estimated -113 degrees C and gets gradually warmer with depth.

These bodies of water are potentially interesting biologically and the researchers wrote that “future missions to Mars should target this region.” 

Earlier this year, a new computer model by NASA scientists lent further support to the theory that the ocean beneath the thick, icy crust of Jupiter’s moon Europa could be habitable.

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Salty lake, ponds may be gurgling beneath South Pole on Mars – CP24 Toronto's Breaking News

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Marcia Dunn, The Associated Press


Published Monday, September 28, 2020 7:46PM EDT

CAPE CANAVERAL, Fla. – A network of salty ponds may be gurgling beneath Mars’ South Pole alongside a large underground lake, raising the prospect of tiny, swimming Martian life.

Italian scientists reported their findings Monday, two years after identifying what they believed to be a large buried lake. They widened their coverage area by a couple hundred miles, using even more data from a radar sounder on the European Space Agency’s Mars Express orbiter.

In the latest study appearing in the journal Nature Astronomy, the scientists provide further evidence of this salty underground lake, estimated to be 12 miles to 18 miles (20 kilometres to 30 kilometres) across and buried 1 mile (1.5 kilometres) beneath the icy surface.

Even more tantalizing, they’ve also identified three smaller bodies of water surrounding the lake. These ponds appear to be of various sizes and are separate from the main lake.

Roughly 4 billion years ago, Mars was warm and wet, like Earth. But the red planet eventually morphed into the barren, dry world it remains today.

The research team led by Roma Tre University’s Sebastian Emanuel Lauro used a method similar to what’s been used on Earth to detect buried lakes in the Antarctic and Canadian Arctic. They based their findings on more than 100 radar observations by Mars Express from 2010 to 2019; the spacecraft was launched in 2003.

All this potential water raises the possibility of microbial life on – or inside – Mars. High concentrations of salt are likely keeping the water from freezing at this frigid location, the scientists noted. The surface temperature at the South Pole is an estimated minus 172 degrees Fahrenheit (minus 113 degrees Celsius), and gets gradually warmer with depth.

These bodies of water are potentially interesting biologically and “future missions to Mars should target this region,” the researchers wrote.

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Another look at possible under-ice lakes on Mars: They’re still there – Ars Technica

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In recent decades, we’ve become aware of lots of water on Earth that’s deep under ice. In some cases, we’ve watched this water nervously, as it’s deep underneath ice sheets, where it could lubricate the sheets’ slide into the sea. But we’ve also discovered lakes that have been trapped under ice near the poles, possibly for millions of years, raising the prospect that they could harbor ancient ecosystems.

Now, researchers are applying some of the same techniques that we’ve used to find those under-ice lakes to data from Mars. And the results support an earlier claim that there are bodies of water trapped under the polar ice of the red planet.

Spotting liquids from orbit

Mars clearly has extensive water locked away in the forum of ice, and some of it cycles through the atmosphere as orbital cycles make one pole or the other a bit warmer. But there’s not going to be pure liquid water on Mars—the temperatures just aren’t high enough for very long, and the atmospheric pressures are far too low to keep any liquid water from boiling off into the atmosphere.

Calculations suggest, however, that liquid water is possible on Mars—just not on the surface. With enough dissolved salts, a water-rich brine could remain liquid at the temperatures prevalent on Mars—even in the polar areas. And if it’s trapped under the Martian surface, there might be enough pressure to keep it liquid despite the thin atmosphere. That surface could be Martian soil, and people are thinking about that possibility. But the surface could also be one of the ice sheets we’ve spotted on Mars.

That possibility helped motivate the design of the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) on the Mars Express orbiter. MARSIS is a radar device that uses wavelengths that water ice is transparent to. As a result, most of the photons that come back to the instrument are reflected by the interface between ice and something else: the atmosphere, the underlying bedrock, and potentially any interface between the ice and a liquid brine underneath it.

And that’s what the original results, published in 2018, seemed to indicate. In an area called Ultimi Scopuli near Mars’ south pole. The researchers saw a bright reflection, distinct from the one caused by the underlying bedrock, at some specific locations under the ice. And they interpreted this as indicating a boundary between ice and some liquid brines.

Now with more data

Two things have changed since those earlier results were done. One is that Mars Express has continued to pass over Mars’ polar regions, generating even more data for analysis. The second is that studies of ice-covered lakes on Earth have also advanced, with new ones identified from orbit using similar data. So some of the team behind the original work decided it was time to revisit the ice sheets at Ultimi Scopuli.

The analysis involves looking at details of the photons reflected back to the MARSIS instrument from a 250 x 300 square kilometer area. One aspect of that is the basic reflectivity of the different layers that can be discerned from the data. Other aspects of the signal can tell us about how smooth the surface of the reflective boundaries are and whether the nature of the boundary changes suddenly.

For example, the transition from an ice-bedrock boundary to an ice-brine one would cause a sudden shift from a relatively weak, uneven signal to a brighter and smoother one.

The researchers generated separate maps of the intensity and the smoothness of the signal and found that the maps largely overlapped, giving them confidence that they were identifying real transitions in the surfaces. A separate measure of the material (called permittivity) showed that it was high in the same location.

Overall, the researchers found that the largest area that’s likely to have water under the ice as about 20 by 30 kilometers. And it’s separated by bedrock features from a number of similar but smaller bodies. Calling these bodies “lakes” is speculative, given that we have no idea how deep they are. But the data certainly is consistent with some sort of under-ice feature—even if we use the standards of detection that have been used for under-ice lakes on Earth.

How did that get there?

The obvious question following the assumption that these bodies are filled with a watery brine is how that much liquid ended up there. We know that these salty solutions can stay liquid at temperatures far below the freezing point. But the conditions on Mars are such that most of minimum temperatures for water to remain liquid are right at the edge of the possible conditions at the site of the polar ice sheets. So some people have suggested geological activity as a possible source of heat to keep things liquid.

That’s not necessarily as unlikely as it may sound. Some groups have proposed that some features indicate that there was magma on the surface of Mars as recently as recently as 2 million years ago. But the researchers here argue that if things are on the edge of working under current climate conditions, there’s no need to resort to anything exceptional.

Instead, they suggest that the sorts of salts we already know are present on Mars can absorb water vapor out of the thin Martian atmosphere. Once formed, these can remain liquid down to 150 Kelvin, when the local temperatures at Ultimi Scopuli are likely to be in the area of 160 Kelvin and increase with depth.

And if that’s true, there could be liquid in many more locations at Mars’ poles. Not all of them are as amenable to orbital imaging as Ultimi Scopuli, but it’s a safe bet that this team will try to find additional ones.

Nature Astronomy, 2020. DOI: 10.1038/s41550-020-1200-6 (About DOIs).

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