Hubble Uncovers Thousands of Globular Star Clusters in Coma

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Hubble Uncovers Thousands of Globular Star Clusters in Coma

Post by bystander » Thu Nov 29, 2018 4:21 pm

Hubble Uncovers Thousands of Globular Star Clusters Scattered among Galaxies
NASA | GSFC | STScI | HubbleSite | 2018 Nov 29
Gazing across 300 million light-years into a monstrous city of galaxies, astronomers have used NASA's Hubble Space Telescope to do a comprehensive census of some of its most diminutive members: a whopping 22,426 globular star clusters found to date.

The survey ... will allow for astronomers to use the globular cluster field to map the distribution of matter and dark matter in the Coma galaxy cluster, which holds over 1,000 galaxies that are packed together.

Because globular clusters are much smaller than entire galaxies – and much more abundant – they are a much better tracer of how the fabric of space is distorted by the Coma cluster's gravity. In fact, the Coma cluster is one of the first places where observed gravitational anomalies were considered to be indicative of a lot of unseen mass in the universe – later to be called “dark matter.”

Among the earliest homesteaders of the universe, globular star clusters are snow-globe-shaped islands of several hundred thousand ancient stars. They are integral to the birth and growth of a galaxy. About 150 globular clusters zip around our Milky Way galaxy, and, because they contain the oldest known stars in the universe, were present in the early formative years of our galaxy.

Some of the Milky Way's globular clusters are visible to the naked eye as fuzzy-looking "stars." But at the distance of the Coma cluster, its globulars appear as dots of light even to Hubble's super-sharp vision. The survey found the globular clusters scattered in the space between the galaxies. They have been orphaned from their home galaxy due to galaxy near-collisions inside the traffic-jammed cluster. Hubble revealed that some globular clusters line up along bridge-like patterns. This is telltale evidence for interactions between galaxies where they gravitationally tug on each other like pulling taffy. ...

A Wide-field Map of Intracluster Globular Clusters in Coma ~ Juan P. Madrid et al
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Re: Hubble Uncovers Thousands of Globular Star Clusters in Coma

Post by saturno2 » Fri Nov 30, 2018 3:59 am

The Coma Group not only has a lot of galaxies,
It also has large number of globular cluster of stars.
But those globular clusters of stars of Coma will have
Very old stars?

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Re: Hubble Uncovers Thousands of Globular Star Clusters in Coma

Post by Ann » Fri Nov 30, 2018 6:50 am

saturno2 wrote:
Fri Nov 30, 2018 3:59 am
The Coma Group not only has a lot of galaxies,
It also has large number of globular cluster of stars.
But those globular clusters of stars of Coma will have
Very old stars?
NGC 1818. Photo (from 1998): HST.
Almost certainly, yes. Because we expect practically all - or maybe all! - globular clusters to be made up of very old stars.


But there is one young "pre-globular cluster" in the Large Magellanic Cloud:

Wikipedia wrote:

NGC 1818 is a young rich star cluster in the Large Magellanic Cloud. It is expected it will become a globular cluster, but is only about 25 million years old while almost all known globular clusters formed billions of years ago.

Chris Peterson, who often makes inputs here at Starship Asterisk* would probably protest and say that NGC 1818 is not a globular cluster and will never become one, because it formed by another mechanism than "true" globular clusters like, for example, 47 Tucanae. Also, NGC 1818 is not at all as rich in stars as most globular clusters in the Milky Way, and then we must remember that clusters always lose members over time, so the globulars of the Milky Way were even richer in their youth than they are now.

Undoubtedly, though, NGC 1818 is a rich young "populous cluster". But there really are other young populous clusters, too:


NGC 6946 with giant cluster.
Giant cluster in NGC 6946. Photo: HST.







Søren Larsen wrote about the rich cluster in NGC 6946:

On the PC image you can see an extremely bright young star cluster (...) with an estimated mass of about 1 million solar masses and an age of about 15 million years.
If it is true that the mass of the giant young cluster in NGC 6946 is about a million solar masses, then it is about twice as massive as the extremely young R136 in the Large Magellanic Cloud.

My point is that very young populous clusters are still forming. We even have one in our own galaxy, NGC 3603.

But populous young clusters form most easily in galaxies with a lot of ongoing star formation, like the Large Magellanic Cloud. NGC 6946 is clearly a galaxy that has seen a lot of star formation in the very recent past. The Milky Way is not a starburst galaxy by any means, but NGC 3603 is classified as a starburst region in our galaxy.

M58. Image credit:
Steve Mandel/Adam Block /NOAO /AURA /NSF.
There really are pockets of star formation in galaxies that are for the most part red and dead. Personally I really, really wonder about the nature of that one prominent blue knot in the mostly non-starforming barred spiral galaxy, M58, in the Virgo Cluster.

As for the Coma Cluster, it is chock full of elliptical galaxies with no star formation in them at all. Admittedly there are a few spirals there, too. NGC 4921 is known for its "anemic" nature, with its dust and spiral arms dissolving into nothingness, so no massive clusters are expected from that galaxy. NGC 4911 has a bit more "oomph" in it, and Wikipedia claims it has a starburst ring, so there might possibly be a rich young populous cluster somewhere in that galaxy.

But apart from something that might be inside NGC 4911, we have every reason to believe that all the huge rich clusters that are found in the Coma Cluster are remnants of that cluster's glory days of star formation in the very distant past.

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Re: Hubble Uncovers Thousands of Globular Star Clusters in Coma

Post by neufer » Fri Nov 30, 2018 5:56 pm


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