Astronomers uncover new galaxy clusters hiding in plain sight

The newly found galaxy cluster CHIPS1911+4455 has a singular twisted form in comparison with different quickly cooling galaxy clusters. This picture was taken with the Hubble Area Telescope. Credit score: NASA/ESA/Hubble Heritage Crew

MIT astronomers have found new and weird galactic neighborhoods that earlier research ignored. Their outcomes, revealed at present, recommend that roughly 1 % of galaxy clusters look atypical and might be simply misidentified as a single vibrant galaxy. As researchers launch new cluster-hunting telescopes, they need to heed these findings or danger having an incomplete image of the universe.


Galaxy clusters comprise a whole lot to 1000’s of galaxies certain collectively by gravity. They transfer by means of a scorching soup of fuel known as the intracluster medium, which comprises extra mass than all the celebrities in all of the galaxies inside it. This scorching fuel fuels star formation because it cools and emits X-ray radiation that we are able to observe with space-based telescopes.

This vibrant fuel cloud creates a fuzzy halo of X-rays round galaxy clusters, making them stand out from extra discrete level sources of X-rays produced by, for instance, a star or quasar. Nevertheless, some galactic neighborhoods break this mould, as MIT Affiliate Professor Michael McDonald realized 9 years in the past.

In 2012, McDonald found a cluster not like some other, which shone vibrant like some extent supply within the X-ray. Its central galaxy hosts a ravenous black gap that consumes matter and spews X-rays so vibrant as to drown out the diffuse radiation of the intracluster medium. In its core, the cluster kinds stars at a charge roughly 500 occasions larger than most different clusters, giving it the blue glow of a younger star inhabitants as a substitute of the standard purple hue of getting older stars.

“We might been searching for a system like this for many years,” McDonald says of the Phoenix cluster. And but, it had been noticed and handed over years prior, assumed to be a single galaxy as a substitute of a cluster. “It’d been within the archive for many years and nobody noticed it. They had been trying previous it as a result of it did not look proper.”

And so, McDonald puzzled, what different uncommon clusters could be lurking within the archive, ready to be discovered? Thus, the Clusters Hiding in Plain Sight (CHiPS) survey was born.

Taweewat Somboonpanyakul, a graduate scholar in McDonald’s lab, devoted his complete Ph.D. to the CHiPS survey. He started by choosing potential cluster candidates from a long time of X-ray observations. He used present knowledge from ground-based telescopes in Hawaii and New Mexico, and visited the Magellan telescopes in Chile to take new photos of the remaining sources, trying to find neighboring galaxies that will reveal a cluster. In probably the most promising instances, he zoomed in with higher-resolution telescopes such because the space-based Chandra X-Ray Observatory and Hubble Area Telescope.

After six years, the CHiPS survey has now come to an in depth. As we speak in The Astrophysical Journal, Somboonpanyakul revealed the survey’s cumulative outcomes, which embody the invention of three new galaxy clusters. One in all these clusters, CHIPS1911+4455, is much like the rapidly-star-forming Phoenix cluster and was described in a paper in January in The Astrophysical Journal Letters. It is an thrilling discovering since astronomers know of only a few different Phoenix-like clusters. This cluster invitations additional examine, nevertheless, because it has a twisted form with two prolonged arms, whereas all different rapidly-cooling clusters are round. The researchers consider it might have collided with a smaller galaxy cluster. “It is tremendous distinctive in comparison with all of the galaxy clusters that we now know,” says Somboonpanyakul.

In all, the CHiPS survey revealed that older X-ray surveys missed roughly 1 % of galactic neighborhoods as a result of they give the impression of being totally different than the standard cluster. This may have important implications, since astronomers examine galaxy clusters to find out about how the universe expands and evolves. “We have to discover all of the clusters to get these issues proper,” McDonald explains. “Ninety-nine % completion is not sufficient if you wish to push the frontier.”

As scientists uncover and examine extra of those uncommon galaxy clusters, they could higher perceive how they match into the broader cosmic image. At this level, they do not know whether or not a small variety of clusters are all the time on this unusual, Phoenix-like state, or if that is maybe a typical section that every one clusters bear for a brief time frame—roughly 20 million years, a fleeting second by spacetime requirements. It is troublesome for astronomers to inform the distinction, as they solely get a single snapshot of every cluster almost frozen in time. However with extra knowledge, they will make higher fashions of the physics governing these galactic neighborhoods.

The conclusion of the CHiPS survey coincides with the launch of a brand new X-ray telescope, eROSITA, which goals to develop our catalog of clusters from a couple of hundred to tens of 1000’s. However until they modify the way in which they search for these clusters, they may miss a whole lot that deviate from the norm. “The individuals which can be constructing out the cluster searches for this new X-ray telescope want to concentrate on this work,” says McDonald. “In case you miss 1 % of the clusters, there is a basic restrict to how nicely you possibly can perceive the universe.”


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Extra data:
Taweewat Somboonpanyakul et al. The Clusters Hiding in Plain Sight (CHiPS) Survey: Full Pattern of Excessive BCG Clusters, The Astrophysical Journal (2021). DOI: 10.3847/1538-4357/abe1bc

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