Wandering Stars Have Been Adrift Between Galaxies for Billions of Years

Hubble Space Telescope images of two massive clusters of galaxies named MOO J1014+0038 (left panel) and SPT-CL J2106-5844 (right panel).. Credits: NASA/ESA/STScI/James Jee (Yonsei University)/Joseph DePasquale (STScI)

In the giant galaxy clusters in the Universe, which can consist of hundreds or thousands of galaxies, there are countless “rogue” stars wandering between them. These stars are not gravitationally bound to any individual galaxy but to the halo of galaxy clusters themselves and are only discernible by the diffuse light they emit – “Ghost Light” or “Intracluster light” (ICL). For astronomers, the explanation for how these stars became so scattered throughout their galaxy clusters has always been an unresolved question.

There are several theories, including the possibility that the stars were pulled from their galaxies, ejected in the course of galactic mergers, or were part of their cluster since its early formation billions of years ago. Using NASA’s Hubble Space Telescope, a team from Yonsei University, Seoul, and the University of California, Davis, conducted an infrared survey of distant galaxy clusters. Their observations suggest that these wandering stars have been adrift for billions of years and were not stripped from their respective galaxies.

Continue reading “Wandering Stars Have Been Adrift Between Galaxies for Billions of Years”

Webb Stares Deeply Into the Universe, Showing How Galaxies Assemble

This image represents a portion of the full PEARLS field, which will be about four times larger. Thousands of galaxies over an enormous range in distance and time are seen in exquisite detail, many for the first time. Image Credit: SCIENCE: NASA, ESA, CSA, Rolf A. Jansen (ASU), Jake Summers (ASU), Rosalia O'Brien (ASU), Rogier Windhorst (ASU), Aaron Robotham (UWA), Anton M. Koekemoer (STScI), Christopher Willmer (University of Arizona), JWST PEARLS Team IMAGE PROCESSING: Rolf A. Jansen (ASU), Alyssa Pagan (STScI)

The James Webb Space Telescope is delivering a deluge of images and data to eager scientists and other hungry-minded people. So far, the telescope has shown us the iconic Pillars of Creation like we’ve never seen them before, the details of very young stars as they grow inside their dense cloaks of gas, and a Deep Field that’s taken over from the Hubble’s ground-breaking Deep Field and Ultra Deep Field images. And it’s only getting started.

True to its main science objectives, the JWST has peered back in time to the Universe’s earliest galaxies looking for clues to how they assemble and evolve.

Continue reading “Webb Stares Deeply Into the Universe, Showing How Galaxies Assemble”

A Black Hole has been Burping for 100 Million Years

Artist view of an active supermassive black hole. Credit: ESO/L. Calçada

Black holes are gluttonous behemoths that lurk in the center of galaxies. Almost everybody knows that nothing can escape them, not even light. So when anything made of simple matter gets too close, whether a planet, a star or a gas cloud, it’s doomed.

But the black hole doesn’t eat it at once. It plays with its food like a fussy kid. Sometimes, it spews out light.

When the black hole is not only at the center of a galaxy but the center of a cluster of galaxies, these burps and jets carve massive cavities out of the hot gas at the center of the cluster called radio bubbles.

Continue reading “A Black Hole has been Burping for 100 Million Years”

Lasers Recreate the Conditions Inside Galaxy Clusters

Galaxies don’t exist in a vacuum. Ok, maybe they do (mostly, since even interstellar space has some matter in it). But galaxies aren’t normally solitary objects. Multiple galaxies interacting gravitationally can form clusters. These clusters can interact with each other, forming superclusters. Our own galaxy is part of a group of galaxies called the Local Group. This Local Group is part of the Virgo Supercluster, which is in turn a part of a group of superclusters called the Laniakea Supercluster.

Mixed in with all of these galaxies is a lot of heat, with extremely high temperatures comparable to the core of our Sun, around 10 million Kelvin (27 million degrees Fahrenheit). This temperature is so hot that hydrogen atoms cannot exist, and instead of gas a plasma forms of protons and electrons. This is a problem for physicists though, who say it shouldn’t be that hot.

As Gianluca Gregori, a professor of physics at University of Oxford and one author of a new paper detailing an experiment to recreate the conditions inside a galaxy cluster, puts it: “The reason why the gas inside the galaxy cluster should have cooled down is simply due to the fact that the cluster has existed for a very long time (for a time which is comparable to the age of the Universe). So, if we assume thermal conduction works in the normal way, we would have expected the initial hot core to have dissipated its heat by now. But observations shows it has not.”

Continue reading “Lasers Recreate the Conditions Inside Galaxy Clusters”

Astronomers see an Enormous Shockwave, 60 Times Bigger Than the Milky Way

Astronomers have a thing for big explosions and collisions, and it always seems like they are trying to one-up themselves in finding a bigger, brighter one.  There’s a new entrant to that category – an event so big it created a burst of particles over 1 billion years ago that is still visible today and is 60 times bigger than the entire Milky Way.

Continue reading “Astronomers see an Enormous Shockwave, 60 Times Bigger Than the Milky Way”

By Measuring Light From Individual Stars Between Galaxy Clusters, Astronomers Find Clues About Dark Matter

dark matter shown in blue
This image from the NASA/ESA Hubble Space Telescope shows the galaxy cluster MACS J0416. This is one of six clusters that was studied by the Hubble Frontier Fields programme, which yielded the deepest images of gravitational lensing ever made. Scientists used intracluster light (visible in blue) to study the distribution of dark matter within the cluster.

Astronomers have been able to measure an extremely faint glow of light within galaxy clusters, and that measurement came with a surprise: it traced the amount of invisible dark matter, something that scientists have been trying to pin down for decades.

Continue reading “By Measuring Light From Individual Stars Between Galaxy Clusters, Astronomers Find Clues About Dark Matter”

Matter makes up exactly 31.5±1.3% of the Universe

dark matter shown in blue
This image from the NASA/ESA Hubble Space Telescope shows the galaxy cluster MACS J0416. This is one of six clusters that was studied by the Hubble Frontier Fields programme, which yielded the deepest images of gravitational lensing ever made. Scientists used intracluster light (visible in blue) to study the distribution of dark matter within the cluster.

Weighing the universe is a tricky task, but a team of astronomers have used a clever technique to measure how many galaxy clusters are in the cosmos, and from there come up with a total amount of matter. The answer: 31.5±1.3% of all the energy in the universe.

Continue reading “Matter makes up exactly 31.5±1.3% of the Universe”

The Universe is the Same, Everywhere We Look. Even More than Cosmologists Predicted

Several superclusters revealed by the 2dF Galaxy Redshift Survey.
Several superclusters revealed by the 2dF Galaxy Redshift Survey.

No matter which direction you look in the Universe, the view is basically the same if you look far enough. Our local neighborhood is populated with bright nebulae, star clusters, and dark clouds of gas and dust. There are more stars toward the center of the Milky Way than there are in other directions. But across millions, and billions, of light-years, galaxies cluster evenly in all directions, and everything starts to look the same. In astronomy, we say the Universe is homogeneous and isotropic. Put another way, the Universe is smooth.

Continue reading “The Universe is the Same, Everywhere We Look. Even More than Cosmologists Predicted”

Complete and Total Mayhem in a Distant Galaxy Collision

The filamentary structures observed by LOFAR at the center of Abell 2255, here reported in red. These radio emissions are due to trails of particles and magnetic fields released by the galaxies during their motion inside the cluster (credits: Botteon et al. (2020) – LOFAR – SDSS).

A cluster of galaxies is nothing trivial. The shocks, the turbulence, the energy, as all of that matter and energy merges and interacts. And we can watch all the chaos and mayhem as it happens.

A team of astronomers are looking at the galaxy cluster Abell 2255 with the European Low-Frequency Array (LOFAR) radio telescope, and their images are showing some never-before-seen details in this actively merging cluster.

Continue reading “Complete and Total Mayhem in a Distant Galaxy Collision”

Astronomers See a Pileup of 14 Separate Galaxies in the Early Universe

Artist impression of 14 galaxies detected by ALMA as they appear in the very early, very distant universe. These galaxies are in the process of merging and will eventually form the core of a massive galaxy cluster. Credit: NRAO/AUI/NSF; S. Dagnello

Looking deep into the observable Universe – and hence, back to the earliest periods of time – is an immensely fascinating thing. In so doing, astronomers are able to see the earliest galaxies in the Universe and learn more about how they evolved over time. From this, they are not only able to see how large-scale structures (like galaxies and galaxy clusters) formed, but also the role played by dark matter.

Most recently, an international team of scientists used the Atacama Large Millimeter-submillimeter Array (ALMA) to observe the Universe when it was just 1.4 billion years old. What they observed was a “protocluster”, a series of 14 galaxies located 12.4 billion light-years away that were about to merge. This would result in the formation of a massive galaxy cluster, one of the largest objects in the known Universe.

The study which described their findings, titled “A massive core for a cluster of galaxies at a redshift of 4.3“, recently appeared in the journal Nature. The study was led by Tim Miller – an astronomer from Dalhousie University, Halifax, and Yale University – and included members from NASA’s Jet Propulsion Laboratory, the European Southern Observatory (ESO), Canada’s National Research Council, the Harvard-Smithsonian Center for Astrophysics, the National Radio Astronomy Observatory, and multiple universities and research institutions.

ALMA image of 14 galaxies forming a protocluster known as SPT2349-56. These galaxies are in the process of merging and will eventually form the core of a truly massive galaxy cluster. Credit: ALMA (ESO/NAOJ/NRAO); B. Saxton (NRAO/AUI/NSF)

As they indicate in their study, this protocluster (designated SPT2349-56) was first observed by the National Science Foundation’s South Pole Telescope. Using the Atacama Pathfinder Experiment (APEX), the team conducted follow-up observations that confirmed that it was an extremely distant galactic source, which was then observed with ALMA. Using ALMA’s superior resolution and sensitivity, they were able to distinguish the individual galaxies.

What they found was that these galaxies were forming stars at rate 1,000 times faster than our galaxy, and were crammed inside a region of space that was about three times the size of the Milky Way. Using the ALMA data, the team was also able to create sophisticated computer simulations that demonstrated how this current collection of galaxies will likely grow and evolve over billion of years.

These simulations indicated that once these galaxies merge, the resulting galaxy cluster will rival some of the most massive clusters we see in the Universe today. As Scott Chapman, and astrophysicist at Dalhousie University and a co-author on the study, explained:

“Having caught a massive galaxy cluster in throes of formation is spectacular in and of itself. But, the fact that this is happening so early in the history of the universe poses a formidable challenge to our present-day understanding of the way structures form in the universe.”

Zooming in to the galaxies discovered by ALMA that are evolving into a galaxy cluster. Credit: ALMA (ESO/NAOJ/NRAO), T. Miller & S. Chapman et al.; Herschel; South Pole Telescope; (NRAO/AUI/NSF) B. Saxton

The current scientific consensus among astrophysicists states that a few million years after the Big Bang, normal matter and dark matter began to form larger concentrations, eventually giving rise to galaxy clusters. These objects are the largest structures in the Universe, containing trillions of stars, thousands of galaxies, immense amounts of dark matter and massive black holes.

However, current theories and computer models have suggested that protoclusters – like the one observed by ALMA – should have taken much longer to evolve. Finding one that dates to just 1.4 billion years after the Big Bang was therefore quite the surprise. As Tim Miller, who is currently a doctoral candidate at Yale University, indicated:

“How this assembly of galaxies got so big so fast is a bit of a mystery, it wasn’t built up gradually over billions of years, as astronomers might expect. This discovery provides an incredible opportunity to study how galaxy clusters and their massive galaxies came together in these extreme environments.”

Looking to the future, Chapman and his colleagues hope to conduct further studies of SPT2349-56 to see how this protoclusters eventually became a galaxy cluster. “ALMA gave us, for the first time, a clear starting point to predict the evolution of a galaxy cluster,” he said. “Over time, the 14 galaxies we observed will stop forming stars and will collide and coalesce into a single gigantic galaxy.”

The study of this and other protoclusters will be made possible thanks to instruments like ALMA, but also next-generation observatories like the Square Kilometer Array (SKA). Equipped with more sensitive arrays and more advanced computer models, astronomers may be able to create a truly accurate timeline of how our Universe became what it is today.

Further Reading: NRAO, Nature