Dark matter flies ahead of normal matter in mega galaxy cluster collision

Astronomers have untangled a messy collision between two huge clusters of galaxies during which the clusters’ huge clouds of dark matter have decoupled from the so-called regular matter. The 2 clusters every include hundreds of galaxies and are situated billions of light-years away from Earth.

As they plowed by way of one another, the dark matter—an invisible substance that feels the drive of gravity however emits no mild—sped forward of the traditional matter. The brand new observations are the primary to straight probe the decoupling of the darkish and regular matter velocities.

Galaxy clusters are among the many largest buildings within the universe, glued collectively by the drive of gravity. Solely 15% of the mass in such clusters is regular matter, the identical matter that makes up planets, individuals, and every little thing you see round you. Of this regular matter, the overwhelming majority is sizzling gasoline, whereas the remainder is stars and planets. The remaining 85% of the cluster mass is dark matter.

Through the tussle that happened between the clusters, identified collectivity as MACS J0018.5+1626, the person galaxies themselves largely went unscathed as a result of a lot space exists between them. However when the large shops of gasoline between the galaxies (the traditional matter) collided, the gasoline turned turbulent and superheated.

Whereas all matter, together with each regular matter and dark matter, interacts by way of gravity, the traditional matter additionally interacts by way of electromagnetism, which slows it down throughout a collision. So, whereas the traditional matter turned slowed down, the swimming pools of dark matter inside every cluster sailed on by way of.

Consider an enormous collision between a number of dump vans carrying sand, suggests Emily Silich, lead writer of a brand new research describing the findings in The Astrophysical Journal. “The dark matter is just like the sand and flies forward,” she says. Silich is a graduate scholar working with Jack Sayers, analysis professor of physics at Caltech and principal investigator of the research.

The invention was made utilizing information from the Caltech Submillimeter Observatory (which was recently removed from its web site on Maunakea in Hawai’i and will likely be relocated to Chile), the W.M. Keck Observatory on Maunakea, NASA’s Chandra X-ray Observatory, NASA’s Hubble Area Telescope, the European Area Company’s now-retired Herschel Area Observatory and Planck observatory (whose affiliated NASA science facilities had been primarily based at Caltech’s IPAC), and the Atacama Submillimeter Telescope Experiment in Chile. Among the observations had been made many years in the past, whereas the total evaluation utilizing all of the datasets happened over the previous couple of years.

Such decoupling of darkish and regular matter has been seen earlier than, most famously within the Bullet Cluster. In that collision, the recent gasoline might be seen clearly lagging behind the dark matter after the 2 galaxy clusters shot by way of one another. The state of affairs that happened in MACS J0018.5+1626 (referred to subsequently as MACS J0018.5) is analogous, however the orientation of the merger is rotated, roughly 90 levels relative to that of the Bullet Cluster.

In different phrases, one of many huge clusters in MACS J0018.5 is flying practically straight towards Earth whereas the opposite one is speeding away. That orientation gave researchers a novel vantagepoint from which to, for the primary time, map out the rate of each the dark matter and regular matter and elucidate how they decouple from one another throughout a galaxy cluster collision.

“With the Bullet Cluster, it is like we’re sitting in a grandstand watching a automobile race and are in a position to seize stunning snapshots of the vehicles shifting from left to proper on the straightaway,” says Sayers. “In our case, it is extra like we’re on the straightaway with a radar gun, standing in entrance of a automobile because it comes at us and are in a position to acquire its pace.”

To measure the pace of the traditional matter, or gasoline, within the cluster, researchers used an observational methodology often called the kinetic Sunyaev-Zel’dovich (SZ) impact. Sayers and his colleagues made the first observational detection of the kinetic SZ effect on a person cosmic object, a galaxy cluster named MACS J0717, again in 2013, utilizing information from CSO (the primary SZ impact observations taken of MACS J0018.5 date again to 2006).

The kinetic SZ impact happens when photons from the early universe, the cosmic microwave background (CMB), scatter off electrons in sizzling gasoline on their method towards us on Earth. The photons endure a shift, known as a Doppler shift, as a result of motions of the electrons within the gasoline clouds alongside our line of sight. By measuring the change in brightness of the CMB as a consequence of this shift, researchers can decide the pace of gasoline clouds inside galaxy clusters.

“The Sunyaev-Zeldovich results had been nonetheless a really new observational software when Jack and I first turned a brand new digicam on the CSO on galaxy clusters in 2006, and we had no thought there can be discoveries like this,” says Sunil Golwala, professor of physics and Silich’s college Ph.D. advisor.

“We sit up for a slew of latest surprises after we put next-generation devices on the telescope at its new residence in Chile.”

By 2019, the researchers had made these kinetic SZ measurements in a number of galaxy clusters, which advised them the pace of the gasoline, or regular matter. That they had additionally used Keck to be taught the pace of the galaxies within the cluster, which advised them by proxy the pace of the dark matter (as a result of the dark matter and galaxies behave equally throughout the collision).

However at this stage within the analysis, the staff had a restricted understanding of the orientations of the clusters. They solely knew that one in all them, MACS J0018.5, confirmed indicators of one thing unusual occurring—the recent gasoline, or regular matter, was touring in the wrong way to the dark matter.

“We had this whole oddball with velocities in reverse instructions, and at first we thought it may very well be an issue with our information. Even our colleagues who simulate galaxy clusters did not know what was occurring,” Sayers says. “After which Emily obtained concerned and untangled every little thing.”

For a part of her Ph.D. thesis, Silich tackled the conundrum of MACS J0018.5. She turned to information from the Chandra X-ray Observatory to disclose the temperature and placement of the gasoline within the clusters in addition to the diploma to which the gasoline was being shocked.

“These cluster collisions are essentially the most energetic phenomena because the Huge Bang,” Silich says. “Chandra measures the acute temperatures of the gasoline and tells us concerning the age of the merger and the way not too long ago the clusters collided.”

The staff additionally labored with Adi Zitrin of the Ben-Gurion College of the Negev in Israel to make use of Hubble information to map the dark matter utilizing a technique often called gravitational lensing.

Moreover, John ZuHone of the Middle for Astrophysics at Harvard & Smithsonian helped the staff simulate the cluster smashup. These simulations had been utilized in mixture with information from the assorted telescopes to finally decide the geometry and evolutionary stage of the cluster encounter. The scientists discovered that, previous to colliding, the clusters had been shifting towards one another at roughly 3000 kilometers/second, equal to roughly 1% of the pace of sunshine.

With a extra full image of what was occurring, the researchers had been in a position to determine why the dark matter and regular matter gave the impression to be touring in reverse instructions. Although the scientists say it is exhausting to visualise, the orientation of the collision, coupled with the truth that dark matter and regular matter had separated from one another, explains the oddball velocity measurements.

Sooner or later, the researchers hope that extra research like this one will result in new clues concerning the mysterious nature of dark matter.

“This research is a place to begin to extra detailed research into the character of dark matter,” Silich says. “We now have a brand new sort of direct probe that reveals how dark matter behaves in a different way from regular matter.”

Sayers, who remembers first gathering the CSO information on this object virtually 20 years in the past, says, “It took us a very long time to place all of the puzzle items collectively, however now we lastly know what is going on on. We hope this results in an entire new solution to research dark matter in clusters.”