The Dark Energy Camera Captures the Remains of an Ancient Supernova

The first written record of a supernova comes from Chinese astrologers in the year 185. Those records say a ‘guest star’ lit up the sky for about eight months. We now know that it was a supernova.

All that remains is a ring of debris named RCW 86, and astronomers working with the DECam (Dark Energy Camera) used it to examine the debris ring and the aftermath of the supernova.

Chinese astrologers recorded SN 185 in The Book of the Later Han, or as the Chinese call it, the Hou Han shu. There’s uncertainty around ancient records of astronomical events, and in the Hou Han shu’s case, the uncertainty is amplified by the fact that it was written 200 years after the events that transpired. Ancient Romans may have recorded the supernova explosion too, but that’s less certain.

Ancient records of celestial events can also be uncertain because of confusion between supernovae and comets. In the Hou Han shu, there’s no record of the guest star moving, and the location the Chinese recorded agrees with the position of RCW 86, the debris ring from the SN. Modern astronomers are pretty sure the Hou Han shu recorded SN 185, especially since modern high-tech observations help confirm it.

This image of the supernova remnant RCW 86 is a composite image from Spitzer, WISE, and Chandra. The ring shape has become less clear over 1800 years, but its location matches the location of SN 185 recorded in the Hou Han shu. Image Credit: By NASA/JPL-Caltech/UCLA – WISE, Public Domain, https://ift.tt/Wfn6KAX

SN 185 exploded more than 8,000 light-years away in the rough direction of our nearest stellar neighbour Alpha Centauri. It’s a fascinating object because astronomers can observe the aftermath of a supernova explosion, one of nature’s most climactic events. RCW 86 is just a tattered remnant of SN 185 now, an increasingly misshapen ring of gas and dust. SN 185 was a Type 1a supernova, and unlike other types of supernovae, it left nothing behind other than the expanding, dissipating ring of debris.

But astronomers didn’t know all that at first. They had to figure it all out, and RCW 86 was misleading because of its size.

Its large size led astronomers to believe that SN 185 was a core-collapse supernova. That type of supernova would take about 10,000 years to form the remnant we see today. So astronomers weren’t certain that RCW 86 was associated with SN 185. The timing was way off by over 8,000 years.

This zoomed-in image shows some of the detail in the wide-field DECam image. Image Credit: CTIO/NOIRLab/DOE/NSF/AURA T.A. Rector (University of Alaska Anchorage/NSF’s NOIRLab), J. Miller (Gemini Observatory/NSF’s NOIRLab), M. Zamani & D. de Martin (NSF’s NOIRLab)

Then in 2006, a study showed that an extremely high expansion velocity was behind RCW 86, meaning it is temporally associated with SN 185. That study was based on x-ray observations. They showed that along some portions of the expanding shell, there was a peculiar mixture of both thermal x-ray radiation and synchrotron x-ray radiation. Simply put, thermal x-rays are generated by heat, and synchrotron x-rays are generated by movement. The presence of synchrotron x-rays suggests a much higher velocity in the shell since charged particles need to travel at relativistic speeds to produce them.

This study corrected RCW 86’s age to about 2,000 years old, right in line with SN 185. “Finally,” the authors of the 2006 paper wrote, “we show that the derived shock velocity strengthens the case that RCW 86 is the remnant of SN 185.”

But that didn’t explain why RCW 86 is expanding so fast. Once again, x-ray data led to an explanation. X-ray observations showed a higher-than-expected level of iron in the remnant shell. Type 1a supernovae produce an excessive amount of iron due to their physics. In fact, two-thirds of the iron in our blood and in the Earth itself was produced by type 1a supernovae. Since type 1a supernova can account for the increased iron, and since RCW 86 is expanding so rapidly, astronomers determined that it is indeed SN 185’s remnant.

A type 1a supernova consists of a binary pair, including a white dwarf and another star that could be anything from another smaller white dwarf to a giant star. As the two get close, the white dwarf siphons off material from the companion star. The white dwarf’s pressure and temperature both rise and the star ejects material at a high velocity. This material forms part of the expanding shell called RCS 86.

In a Type Ia supernova, a white dwarf (left) draws matter from a companion star until its mass hits a limit which leads to collapse and then an explosion. Credit: NASA

But unlike a main sequence star, which can expand and cool to compensate, the white dwarf keeps getting hotter until it eventually explodes. The previously ejected material created an empty shell around the white dwarf that made room for the material from the supernova explosion to expand. The result, 1800 years later, is the tattered, bedraggled ring of debris that we see today.

Of course, the ancients had no idea about any of this. They just witnessed a blazing light in the sky that shone for 8 months and then disappeared. Who knows what impact it had on regular people?

It’s fascinating when modern astronomy intersects with what the ancients saw. It’s like a one-way conversation between the past and the future. SN 185/RCW 86 is just one example of it.

A 2021 study examined ancient literature for 3,000 years of records of auroras to help understand Earth’s magnetosphere over time. A 2018 paper showed that a meteor explosion over the Dead Sea 3,700 years ago could explain the Biblical story of Sodom. There are lots of other examples.

Thanks to modern observing capabilities, we can untangle the complex physics behind things like supernovae and understand them in detail. The Dark Energy Camera’s wide-angle image makes it easy for us to relate to them. The aftermath is spread across our screens in intriguing detail.

If you want to go even deeper, download the full-size .tif from NOIRLab’s website.

More:

• Press Release: Supernova From the Year 185: A Rare View of the Entirety of This Supernova Remnant
• 2006 paper: THE X-RAY SYNCHROTRON EMISSION OF RCW 86 AND THE IMPLICATIONS FOR ITS AGE
• Universe Today: Ancient Coin Discovery With An Astronomical Mystery

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A Mysterious Blob Near the Milky Way’s Supermassive Black Hole Might Finally Have an Explanation

At the center of the Milky Way, there is a massive persistent radio source known as Sagittarius A*. Since the 1970s, astronomers have known that this source is a supermassive black hole (SMBH) roughly 4 million times the mass of our Sun. Thanks to advancements in optics, spectrometers, and interferometry, astronomers have been able to peer into Galactic Center. In addition, thanks to the international consortium known as the Event Horizon Telescope (EHT), the world got to see the first image of Sagittarius A* (Sgr A*) in May 2022.

These efforts have allowed astronomers and astrophysicists to characterize the environment at the center of our galaxy and see how the laws of physics work under the most extreme conditions. For instance, scientists have been observing a mysterious elongated object around the Sgr A* (named X7) and wondered what it was. In a new study based on two decades’ worth of data, an international team of astronomers with the UCLA Galactic Center Group (GCG) and the Keck Observatory have proposed that it could be a debris cloud created by a stellar collision.

The research effort was led by the Galactic Center Initiative, an international project made up of scientists from the Mani L. Bhaumik Institute for Theoretical Physics, the University of California Los Angeles (UCLA), the W. M. Keck Observatory, the Observatoire de Paris (Sorbonne Universite), the University of California Berkeley, and the Instituto de Astrofísica de Andalucía (CSIS). The paper that describes their findings recently appeared in The Astrophysical Journal.

Using the Keck Observatory’s 10-meter (32.8 ft) Telescopes on Mauna Kea, the GCG team has been measuring the star closest to Sgr A* (S0-2) for more than twenty years (since 1995). They are one of only two groups in the world to have observed S0-2 make a full orbit of Sgr A* – a process that takes 16 years – for the sake of testing Einstein’s Theory of General Relativity. The team has spent that same time monitoring the object known as X7, a dust and gas cloud of about 50 Earth masses that takes 170 years to orbit the SMBH.

As they report in their study, X7 has become elongated and stretched by tidal forces as it has been pulled closer to Sag A*. Within the next few decades, they anticipate that X7 will disintegrate as the dust and gas that make it up are accreted onto the face of the SMBH. As Anna Ciurlo, a UCLA assistant researcher and the paper’s lead author, said in a UCLA press release:

“No other object in this region has shown such an extreme evolution. It started off comet-shaped and people thought maybe it got that shape from stellar winds or jets of particles from the black hole. But as we followed it for 20 years, we saw it becoming more elongated. Something must have put this cloud on its particular path with its particular orientation.”

The team also notes that X7 has similar properties to other strange dusty objects orbiting Sag A* (aka. G objects). These objects look like dust clouds but behave like stars and were identified using 12 years of spectroscopic measurements made using Keck’s OH-Suppressing Infrared Imaging Spectrograph (OSIRIS). The results of this study (also led by Ciurlo) were presented in 2018 at the 232nd American Astronomical Society Meeting. However, X7’s shape and velocity have changed more dramatically than Gobjects, reaching speeds of up to 1,126.5 km/s (700 mps).

The twin Keck telescopes shoot their laser guide stars into the heart of the Milky Way on a beautifully clear night on the summit of Mauna Kea. Credit: keckobservatory.org/Ethan Tweedie

These results are the most robust analysis to date of X7’s changes in appearance, shape, and behavior and the first estimate of X7’s slightly elliptical orbit. While the origins of X7 are still the subject of debate, the team’s finding suggests that it resulted from a collision between two stars orbiting Sgr A*. Such mergers are very common, especially in the vicinity of black holes. This merger is likely to have ejected gas and dust, which could have formed a shell that is concealing the merged star while the rest became the X7 object.

“The stars circle each other, get closer, merge, and the new star is hidden within a cloud of dust and gas,” said Ciurlo. “X7 could be the dust and gas ejected from a merged star that’s still out there somewhere.” Said Randy Campbell, the science operations lead at the Keck Observatory and a co-author of the paper:

“It’s exciting to see significant changes of X7’s shape and dynamics in such great detail over a relatively short time scale as the gravitational forces of the supermassive black hole at the center of the Milky Way influences this object. It’s a privilege to be able to study the extreme environment at the center of our galaxy. This study can only be done using Keck’s superb capabilities, and performed at the very special and revered Maunakea, with honor and respect to the mauna.”

Based on its trajectory, the team estimates that X7 will make its closest approach to Sgr A* sometime in 2036 and then spiral inward to be devoured. In the meantime, the research team will continue to monitor X7 using the Keck Observatory and watch as the powerful gravity of Sgr A* pulls it apart.

Further Reading: UCLA, The Astrophysical Journal

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Blue Origin is Building Solar Cells out of (Simulated) Lunar Regolith

Power infrastructure will be critical for any long-term space colony, and one of the most critical pieces of that power infrastructure, at least in the inner solar system, is solar cells. So in-situ research experts were thrilled when Blue Origin, ostensibly a rocket company, recently announced that they had made functional solar cells entirely out of nothing other than lunar regolith simulant. 

The process, which the aptly named Blue Alchemist, has been in the works for some time. According to a press release, Blue Origin has been working on making solar cells and necessary support components, such as wire and cover glass, all from regolith since 2021.

At its heart is a relatively simple process – molten regolith electrolysis. Basically, that means that blue origin uses electricity to split constituent atoms from the oxygen they are bound to in the lunar soil. Normal electrolytic cells separate water into hydrogen and oxygen, but Blue Alchemist takes the process a step further and separates elements such as iron, aluminum, and, most importantly, silicon from the oxygen they are bound to on the lunar surface.

YouTube video discussing the Blue Alchemist project
Credit – Angry Astronaut YouTube Channel

One advantage of this process is that the “waste” product is oxygen – itself an invaluable material for lunar exploration, both as a component of breathable air, but also a potential rocket fuel. Silicon is the basis for not only solar cells but also glass, which needs to cover solar cells on the Moon to allow them to last more than a few days in the harsh radiative lunar environment. And iron and aluminum are useful for structural materials and conductive wire, in aluminum’s case. All this comes from the “dirt” that completely covers the surface of the Moon.

Blue Origin went so far as to make their own lunar regolith simulant to prove their process works rather than buying one already commercially available. They seemed to think that the commercially available simulants were too similar to a mish-mash of “lunar-relevant oxides” that didn’t truly represent the material found in the samples brought back by the Apollo mission and others.

Whatever their inputs, their process seems impressive, resulting in 99.999% pure silicon of the type used to make effective solar cells. Even more impressively, they did all of this “with zero carbon emissions, no water, and no toxic ingredients or other chemicals.” As the company rightfully points out, that kind of process could be useful even here on Earth if they find enough of a supply of oxides similar to those on the Moon.

UT video on a competing technology – printed perovskite panels.

But for now, this is a considerable step forward in the ISRU space. If used properly, it will form the basis of power infrastructure throughout most, if not all, of the lunar power infrastructure that long-term human exploration programs will need. That in itself is impressive enough, notwithstanding any benefits, it might have back here on our own blue marble.

Learn More:
Blue Origin – Blue Alchemist Technology Powers our Lunar Future
UT – Power on the Moon. What Will it Take to Survive the Lunar Night?
UT – Artemis Astronauts Could Rely on Solar Cells Made out of Moon Dust
UT – How do you get Power into Your Lunar Base? With a Tower of Concrete Several Kilometers High

Lead Image:
A picture of the Blue Alchemist solar cell.
Credit – Blue Origin

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Spectacular Night Launch Sends SpaceX Crew 6 to the Space Station

The NASA/SpaceX Crew 6 members are now on their way to the International Space Stations after a spectacular nighttime liftoff from Launch Complex 39A at Kennedy Space Center.

At 12:34 am EST, a SpaceX Falcon 9 rocket sent a Dragon spacecraft named Endeavour into orbit. Onboard were NASA astronauts Stephen Bowen and Warren Hoburg, along with United Arab Emirates (UAE) astronaut Sultan Alneyadi and Roscosmos cosmonaut Andrey Fedyaev.

Liftoff! Dragon takes flight!#Crew6 launched at 12:34am ET (0534 UTC) March 2, lighting up the skies as the crew heads to orbit in the @SpaceX Dragon Endeavour spacecraft. pic.twitter.com/lEgqJmRu76

— NASA (@NASA) March 2, 2023

“Just want to say, as a rookie flyer, that was one heck of ride. Thank you!” Hoburg radioed back to Earth after Dragon successfully separated from the Falcon 9 rocket. “It’s an absolute miracle of engineering, and I just feel so lucky that I get to fly on this amazing machine.”

The crew is expected to dock to the ISS about 25 hours after the launch, at about 1:17 a.m., Friday, March 3, and have planned mission on the ISS for approximately 6 months.

Roscosmos cosmonaut Andrey Fedyaev, left,NASA astronaut Warren “Woody” Hoburg, second from left, NASA astronaut Stephen Bowen, second from right, and UAE (United Arab Emirates) astronaut Sultan Alneyadi, right, wearing SpaceX spacesuits, are seen as they prepare to depart the Neil A. Armstrong Operations and Checkout Building for Launch Complex 39A to board the SpaceX Dragon spacecraft for the Crew-6 mission launch, on Wednesday, March 1, 2023. Credit: NASA/Joel Kowsky.

Crew-6 will join Expedition 68, consisting of NASA astronauts Frank Rubio, Nicole Mann, and Josh Cassada, as well as JAXA (Japan Aerospace Exploration Agency) astronaut Koichi Wakata, and Roscosmos cosmonauts Sergey Prokopyev, Dmitri Petelin, and Anna Kikina. For a short time, the 11 crew members will live and work in space together until Crew-5 members Mann, Cassada, Wakata, and Kikina return to Earth a few days later.

This is the ninth overall crewed flight for SpaceX, and its sixth operational mission for NASA’s Commercial Crew program.

A SpaceX Falcon 9 rocket carrying the company’s Dragon spacecraft is launched on NASA’s SpaceX Crew-6 mission to the International Space Station on March 2, 2023. Credit: NASA/Joel Kowsky.

During their time on orbit, Crew 6 will conduct hundreds of science experiments and technology?demonstrations. Experiments include studies of how particular materials burn in microgravity, tissue chip research on heart, brain, and cartilage functions, and an investigation that will collect microbial samples from the outside of the space station.

“For more than two decades, humans have continuously lived and worked aboard the International Space Station,” said Kathryn Lueders, associate administrator for NASA’s Space Operations Mission Directorate in Washington. “Commercial Crew Program missions like Crew-6 are essential so we can continue to maximize the important research possible only in the space station’s unique microgravity environment. Congratulations to the NASA and SpaceX teams on a successful launch! I am looking forward to seeing the crew safely aboard the station.”

Keep tabs on the mission at the Crew 6 Mission blog.

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JWST Sees the Same Supernova Three Times in an Epic Gravitational Lens

The NASA/European Space Agency (ESA)/Canadian Space Agency (CSA) James Webb Space Telescope (JWST) mission continues to dazzle and amaze with every image it beams back to Earth, and a recent observation depicting not one, not two, but three images of the same galaxy has been no different, as they proudly tweeted on February 28, 2023.

But how can JWST observe three images of the same object at once? This is done thanks to a phenomenon known as gravitational lensing, which happens when light is bent or warped around a massive celestial object that emits an enormous amount of gravity, most commonly a star like our Sun, but can also happen with massive galaxies, as well.

The triple-imaged object in question is a supernova-hosting galaxy whose light is being distorted and bent by the massive galaxy cluster known as RX J2129, which is located approximately 3.2 billion light years from Earth. Astronomers have determined the three separate images are all different ages given the varying brightness of the supernova depicted in each one. The characteristics of each image also vary due to the uneven mass of the distant galaxy whose light traveled at different distances to reach us.

Triples is best.

This Webb image features a special galaxy that appears 3 times. Why? There's a galaxy cluster here whose mass and gravity are so great that time and space around it gets warped. This magnifies, multiplies, and distorts galaxies behind it: https://t.co/ftRTPC4bDr pic.twitter.com/fzTjUGc5UO

— NASA Webb Telescope (@NASAWebb) February 28, 2023

The oldest image containing the astronomical transient (aka supernova candidate), AT 2002riv, has been determined to be a Type Ia supernova and is identified by the two parallel lines on either side of it. This is followed by an image as the distant galaxy appears ~320 later, and the third image is how it appeared ~1000 days post-AT 2002riv. Both images occurring ~320 and ~1000 days after the first image show the supernova completely gone from view. Type Ia supernova are particularly helpful to astronomers as studying their luminosity can help measure the enormous astronomical distances to them.

“The almost uniform luminosity of a Type Ia supernova could also allow astronomers to understand how strongly the galaxy cluster RX J2129 is magnifying background objects, and therefore how massive the galaxy cluster is,” explains the European Space Agency. “As well as distorting the images of background objects, gravitational lenses can cause distant objects to appear much brighter than they would otherwise. If the gravitational lens magnifies something with a known brightness, such as a Type Ia supernova, then astronomers can use this to measure the ‘prescription’ of the gravitational lens.”

As stated, gravitational lensing is when the gravitational field of a massive celestial object causes background light to appear bent or warped when it comes into view, meaning the celestial object acts a sort of celestial lens so astronomers can view other objects behind it. In this case, a supernova-hosting galaxy whose light has been not only bent but split three times as its light traveled through the “lens” of RX J2129.

Artist’s conception of gravitational lensing of a galaxy. The large object depicted in the center would be RX J2129 and the “lensed gravity images” would be the split images of the supernova-hosting galaxy. (Credit: NASA, ESA & L. Calcada)

Gravitational lensing is one of the most historic predictions of Albert Einstein’s theory of general relativity, and was first discovered in 1979 when two quasars were observed to be in close proximity to each other, but turned out to be the same object whose light had been split in two, similar to what RX J2129 did to the distant galaxy in the recent JWST observation. While gravitational lensing is used to observe large objects like supernovae, a method known as gravitational microlensing is equally used to find exoplanets.

How many more supernovae will JWST observe, and what else will we learn about gravitational lensing in the coming years and decades? Only time will tell, and this is why we science!

As always, keep doing science & keep looking up!

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Remember the DART impact? Hubble Made a Movie of the Debris

When NASA crashed a 610 kg (1,340 lb) impactor into tiny Dimorphos, a moon of the asteroid Didymos, it was all part of an effort to defend Earth. The impact showed how asteroids respond to impacts, and the data is helping NASA prepare for the day when we have to redirect an asteroid away from an eventual impact with Earth.

NASA’s DART (Double Asteroid Redirection Test) smashed into Dimorphos on the 26th of September, 2022, and ground telescopes watched the result.

DART was a success. The impact lowered Dimorphos’ orbital speed and reduced its orbital radius. DART also changed Didymos’ trajectory and excavated a crater on the Dimorphos’ surface that ejected more than 900,000 kg (990 US tons) of debris into space.

The Hubble Space Telescope got in on the action and captured images several hours apart until about 18 days after the impact.

There’s a little bit of mystery in the debris. At first, debris moves away from the impact in straight lines. It’s travelling at about 6.5 kph (4 mph.) That’s fast enough to escape Dimorphos’ weak gravity and prevent it from falling back to the surface. The debris takes on a cone shape with long filaments. (The straight spikes coming from the center of the images are Hubble optic artifacts.)

Immediately after impact, the debris formed a cone shape with long, stringy filaments. Image Credit: NASA, ESA, STScI, J. Li (PSI)

17 hours after the impact, the debris changes. In this second stage, the gravitational interactions between Didymos and Dimorphos start to distort the ejecta’s cone shape. Rotating, pin-wheeled features form, their rotation anchored to Didymos’ gravitational pull.

A few hours after the impact, gravity starts to warp the ejecta stream. Image Credit: NASA, ESA, STScI, J. Li (PSI)

Next, the debris is swept back into a shape like a comet’s tail by the Sun’s radiative pressure on the tiny particles in the ejecta. The debris stretches out further, with the lightest particles the furthest from the asteroid. Then, mysteriously, the debris tail breaks into two tails.

After a few days, the Sun started to affect the debris. The Sun’s radiative pressure stretched the debris out into a comet-tail-like stream. Eventually, the stream split into two. Image Credit: NASA, ESA, STScI, J. Li (PSI)

The Hubble people created a time-lapse movie of the impact and the aftermath. The movie begins about 1.5 hours before the impact and ended 18 days post-impact.

NASA and the ESA aren’t done with DART, Didymos, and Dimorphos yet. In 2024, the ESA will launch their Hera mission, which will arrive at Didymos in December 2026. Hera will undertake a detailed study of Dimorphos to understand more deeply how the impact affected it. Hera will help turn the DART mission into data we can use to protect ourselves from asteroid impacts.

This artist’s illustration shows the ESA’s Hera spacecraft performing close proximity operations at Didymos. The mission will launch in 2024 and reach the double-asteroid in December 2026. Image Credit: By ESA – Science Office, CC BY-SA IGO 3.0, CC BY-SA 3.0 igo, https://ift.tt/8GUbKHQ

Hera is also a technology demonstration mission. It’ll test things like autonomous navigation around an asteroid and low-gravity proximity operations. The mission will also be the first to rendezvous with a double asteroid.

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Hubble Sees an Epic Merger of Three Galaxies

When is 50,000 light-years only a small distance? When three galaxies are that close to one another. At that range, they’re fiercely interacting.

In the case of the three galaxies referred to as SDSSCGB 10189, they’re 50,000 light-years apart and growing closer as they merge into a single massive galaxy.

Galaxy mergers aren’t exotic. The Hubble has caught many galaxies in the act of merging. Our own Milky Way galaxy is in on the game, as it slowly absorbs the Large and Small Magellanic Clouds. Another one of our neighbours, the Sagittarius Dwarf Spheroidal Galaxy (SDSG), is also in the process of merging and has passed through the Milky Way’s disk several times, losing mass each time.

This image based on Gaia data shows the Milky Way’s disk and the location of the Sagittarius Dwarf Galaxy and the Large and Small Magellanic Clouds. All three are slowly merging with the Milky Way. Image Credit: By ESA/Gaia/DPAC, CC BY-SA 3.0 igo, https://ift.tt/msaKki5

While those are all technically mergers, they’re really more like absorptions since the Milky Way is so much more massive than the Magellanic Clouds and the SDSG. Even after the Milky Way has consumed all three, our galaxy will still look pretty much the same.

Things play out differently when three massive galaxies collide, like in the Hubble image. After they merge, they’ll be one single, massive galaxy, probably an elliptical. But while they merge, they’ll wreak gravitational carnage on each other, streaming tails of gas out into space and triggering widespread star formation.

Astronomers research galaxy mergers because they play a key role in the Universe. The modern Universe contains a vast number of huge galaxies, but scientists think they only grew so large through mergers. (Although recent results from the JWST suggest that there were some massive galaxies in the Universe’s first few hundred million years.)

The Hubble has spotted lots of mergers between two massive galaxies. The image montage below is from the Hubble imaging Probe of Extreme Environments and Clusters (HiPEEC), a survey investigating star cluster formation in the extreme environments of six merging galaxies. These images show pairs of galaxies merging.

The Hubble has imaged lots of merging galaxies over the years. Galaxy mergers are spectacular events that trigger abundant star formation. Top left: NGC 3256 Credit: ESA/Hubble, NASA Top Middle: NGC 1614 Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA)-ESA/Hubble Collaboration and A. Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University) Top Right: NGC 4194, also known as the Medusa merger. Credit: ESA/Hubble & NASA, A. Adamo Bottom Left: NGC 3690 consists of a pair of galaxies, dubbed IC 694 and NGC 3690, which made a close pass some 700 million years ago. Bottom Middle: NGC 6052 Image Credit: ESA/Hubble & NASA, A. Adamo et al. Bottom Right: NGC 34 Image Credit: ESA/Hubble & NASA, A. Adamo et al.

Triple galaxy mergers are rare, but Hubble has still spotted some. In February 2022, the Hubble team released an image of IC 2431, another distant trio of merging galaxies about 682 million light-years away. The center of the image is obscured by dust, but the three galaxies are still clearly visible as they interact gravitationally with each other.

IC 2431 is another triple galaxy merger almost 700 million light-years away. The tidal distortions are obvious in this image, and the merger is also triggering star formation. Image Credit: ESA/Hubble & NASA, W. Keel, Dark Energy Survey, DOE, FNAL, DECam, CTIO, NOIRLab/NSF/AURA, SDSS
Acknowledgement: J. Schmidt

The leading image is from an effort to understand the most massive, brightest galaxies in the Universe. They’re called Brightest Cluster Galaxies (BCGs), and they’re the brightest galaxies in any given galaxy cluster. Some BCGs are 100 billion times more massive than our Sun, and most of them are ellipticals. BCGs are found at the kinematic and geometric center of their host cluster.

Galaxy mergers will restructure our little corner of the Universe over long periods of time. The Milky Way is in the Local Group of galaxies, along with another large spiral galaxy, Andromeda. In a few billion years, the pair will merge and form a single galaxy (Milkdromeda?) The Local Group also contains about 50 smaller galaxies and thousands of globular clusters. It’s arranged in a kind of dumbbell shape, with the Milky Way and its satellites in one lobe and Andromeda and its satellites in the other lobe.

This illustration shows the Local Group. The Milky Way is in the center, and Andromeda (M31) is the red galaxy up and to the left. Eventually, the two will merge, along with all of their satellites, into one gigantic elliptical galaxy. Image Credit: By Antonio Ciccolella – Own work, CC BY-SA 4.0, https://ift.tt/PXUjFDo

In a few tens of billions of years, all of the objects in the Local Group will be combined into one gigantic elliptical galaxy. When Hubble spots triple-galaxy mergers, they’re just snapshots of this epic process of merging and combining matter. When will it end?

It’s tempting to think that matter will keep combining into more and more massive agglomerations. But that’s not what will happen. Gravity is ultra-powerful, and if it were left to its own devices, it might eventually gather all matter together into one super-gigantic, ultra-turbo-massive elliptical galaxy. But gravity isn’t ultra-powerful, and it’s not alone.

The Universe is expanding, driven by Dark Energy, gravity’s counterbalance. On smaller scales, gravity can work its magic on regions of the Universe that have over-densities of matter. These over-densities date back to the Big Bang. But on larger scales, these over-densities are defeated by Dark Energy. As long as Dark Energy keeps driving the expansion of the Universe, gravity can never achieve ultimate victory. It can never unify all matter.

Our Local Group is massive, but it’s still small enough to belong to an even larger structure called the Virgo Supercluster. The Universe is full of these superclusters that exist in a sort of web-like arrangement of filaments and clumps. They’re truly vast, and the Virgo Supercluster spans some 110 million light years. At those great distances, gravity is severely weakened. It has no power to reshape superclusters like Virgo.

It doesn’t end there. We can zoom out even further and see that the Virgo Supercluster is part of another structure called the Laniakea Supercluster.

The Laniakea Supercluster with our Local Group (blue) in the center. Image Credit: By Andrew Z. Colvin – Own work, CC BY-SA 4.0, https://ift.tt/VJlniNZ

The Universe’s continuous expansion is like a line in the sand for gravity. It simply can’t overcome it. The large-scale structure of the Universe shows why.

Image of the large-scale structure of the Universe, showing filaments and voids within the cosmic structure. The distances are so vast that gravity can’t draw all this matter together. Credit: Millennium Simulation Project

When we zoom back into the Milky Way, it seems small in comparison. Even the triple merger in the leading Hubble image seems small in comparison, and there are hundreds of billions of stars—maybe even more—involved in that merger, and who knows how many more tens or hundreds of thousands more stars are being born as a result. Don’t even try to guess the number of planets involved and if one of them might host life.

Take another look at these three merging galaxies and consider the vast scale of the Universe. Image Credit: ESA/Hubble & NASA, M. Sun

It’s highly unlikely that humanity will be around when these three galaxies finally combine into a single enormous elliptical galaxy. The same goes for the Milky Way and Andromeda merger. It’s highly unlikely that Earth will even be here since the Sun may have consumed it in its red giant phase.

But for those of us alive now and into the near future, we can gaze out into the Universe with our powerful space telescopes and watch it all unfolding.

More:

• Press Release: Hubble Views a Merging Galactic Trio
• Wikipedia: Galaxy Merger
• Universe Today: Galaxy Mergers can Boost Star Formation, and it can Also Shut it Down

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