Hubble Finds Relic Galaxy Close to Home

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Hubble Finds Relic Galaxy Close to Home

Post by bystander » Mon Mar 12, 2018 8:55 pm

Arrested Development: Hubble Finds Relic Galaxy Close to Home
NASA | GSFC | STScI | HubbleSite | 2018 Mar 12
stsci-h-p1817c-f.jpg
NGC 1277 -- Credits: NASA, ESA, and M. Beasley (IAC)
Ghostly-Looking Galaxy Stopped Making Stars Long Ago

The adventuring cinema archeologist Indiana Jones would be delighted to find a long-sought relic in his own backyard. Astronomers have gotten lucky enough to achieve such a quest. They identified a very rare and odd assemblage of stars that has remained essentially unchanged for the past 10 billion years. The diffuse stellar island provides valuable new insights into the origin and evolution of galaxies billions of years ago.

As far as galaxy evolution goes, this object is clearly a case of “arrested development.” The galaxy, NGC 1277, started its life with a bang long ago, ferociously churning out stars 1,000 times faster than seen in our own Milky Way today. But it abruptly went quiescent as the baby boomer stars aged and grew ever redder. Though Hubble has seen such “red and dead” galaxies in the early universe, one has never been conclusively found nearby. Where the early galaxies are so distant, they are just red dots in Hubble deep-sky images. NGC 1277 offers a unique opportunity to see one up close and personal.

The telltale sign of the galaxy’s state lies in the ancient globular clusters that swarm around it. Massive galaxies tend to have both metal-poor (appearing blue) and metal-rich (appearing red) globular clusters. The red clusters are believed to form as the galaxy forms, while the blue clusters are later brought in as smaller satellites are swallowed by the central galaxy. However, NGC 1277 is almost entirely lacking in blue globular clusters. The red clusters are the strongest evidence that the galaxy went out of the star-making business long ago. However, the lack of blue clusters suggests that NGC 1277 never grew further by gobbling up surrounding galaxies.

A single population of red globular clusters around the massive compact galaxy NGC 1277 - Michael A. Beasley et al
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Ann
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Re: Hubble Finds Relic Galaxy Close to Home

Post by Ann » Mon Mar 12, 2018 11:48 pm

bystander wrote:
Mon Mar 12, 2018 8:55 pm
Arrested Development: Hubble Finds Relic Galaxy Close to Home

The adventuring cinema archeologist Indiana Jones would be delighted to find a long-sought relic in his own backyard. Astronomers have gotten lucky enough to achieve such a quest. They identified a very rare and odd assemblage of stars that has remained essentially unchanged for the past 10 billion years. The diffuse stellar island provides valuable new insights into the origin and evolution of galaxies billions of years ago.

As far as galaxy evolution goes, this object is clearly a case of “arrested development.” The galaxy, NGC 1277, started its life with a bang long ago, ferociously churning out stars 1,000 times faster than seen in our own Milky Way today. But it abruptly went quiescent as the baby boomer stars aged and grew ever redder. Though Hubble has seen such “red and dead” galaxies in the early universe, one has never been conclusively found nearby. Where the early galaxies are so distant, they are just red dots in Hubble deep-sky images. NGC 1277 offers a unique opportunity to see one up close and personal.

The telltale sign of the galaxy’s state lies in the ancient globular clusters that swarm around it. Massive galaxies tend to have both metal-poor (appearing blue) and metal-rich (appearing red) globular clusters. The red clusters are believed to form as the galaxy forms, while the blue clusters are later brought in as smaller satellites are swallowed by the central galaxy. However, NGC 1277 is almost entirely lacking in blue globular clusters. The red clusters are the strongest evidence that the galaxy went out of the star-making business long ago. However, the lack of blue clusters suggests that NGC 1277 never grew further by gobbling up surrounding galaxies.
I'm quite surprised at this.

Yes, the Milky Way's largest globular cluster, "blue" Omega Centauri, is widely considered to have been "stolen" from an unfortunate dwarf galaxy. And our galaxy's second largest globular, "red" 47 Tucanae, is a "homegrown" cluster, for all I know.

But what about the rest of our galaxy's at least 150 globulars? I believe that most of them are "blue", that is, they are so metal-poor that they contain a distinct population of pulsating RR Lyrae stars, which are only found in the most metal-poor clusters. "Red" 47 Tuc lacks them.

Does that mean that a majority of our galaxy's globulars were "stolen"? And the Milky Way has been unable to form many globulars on its own? I find that a bit hard to swallow.

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Re: Hubble Finds Relic Galaxy Close to Home

Post by neufer » Tue Mar 13, 2018 3:48 am

Ann wrote:
Mon Mar 12, 2018 11:48 pm
bystander wrote:
Mon Mar 12, 2018 8:55 pm

The telltale sign of the galaxy’s state lies in the ancient globular clusters that swarm around it. Massive galaxies tend to have both metal-poor (appearing blue) and metal-rich (appearing red) globular clusters. The red clusters are believed to form as the galaxy forms, while the blue clusters are later brought in as smaller satellites are swallowed by the central galaxy. However, NGC 1277 is almost entirely lacking in blue globular clusters. The red clusters are the strongest evidence that the galaxy went out of the star-making business long ago. However, the lack of blue clusters suggests that NGC 1277 never grew further by gobbling up surrounding galaxies.
I'm quite surprised at this.

Yes, the Milky Way's largest globular cluster, "blue" Omega Centauri, is widely considered to have been "stolen" from an unfortunate dwarf galaxy. And our galaxy's second largest globular, "red" 47 Tucanae, is a "homegrown" cluster, for all I know.

But what about the rest of our galaxy's at least 150 globulars? I believe that most of them are "blue", that is, they are so metal-poor that they contain a distinct population of pulsating RR Lyrae stars, which are only found in the most metal-poor clusters. "Red" 47 Tuc lacks them.

Does that mean that a majority of our galaxy's globulars were "stolen"? And the Milky Way has been unable to form many globulars on its own? I find that a bit hard to swallow.
The two populations of globular clusters are BOTH "blue/metal-poor"; it's just that the Oosterhoff type I (OoI) population is not quite as "blue/metal-poor" the Oosterhoff type II (OoII) population. "About a quarter of the globular cluster population in the Milky Way may have been accreted along with their host dwarf galaxy" including relatively metal rich (OoI) globular clusters like Terzan 7.
https://en.wikipedia.org/wiki/Globular_cluster wrote:
<<Globular clusters are generally composed of hundreds of thousands of low-metal, old stars. Some globular clusters, like Omega Centauri in the Milky Way and G1 in M31, are extraordinarily massive, with several million solar masses and multiple stellar populations. Both can be regarded as evidence that supermassive globular clusters are in fact the cores of dwarf galaxies that are consumed by the larger galaxies. About a quarter of the globular cluster population in the Milky Way may have been accreted along with their host dwarf galaxy.

Globular clusters normally consist of Population II stars, which have a low proportion of elements other than hydrogen and helium when compared to Population I stars such as the Sun.
Click to play embedded YouTube video.
:arrow: Terzan 5 has one of the highest metallicities among the Milky Way's globular clusters—[Fe/H]=−0.21. In 2009 it was discovered that Terzan 5 consists of at least two generations of stars with ages of 12 and 4.5 billion years and slightly different metallicities, possibly indicating that it is the core of a disrupted dwarf galaxy, not a true globular cluster. There are only a few other globular clusters in the Milky Way that contain stars with different ages. Among them are M54 and Omega Centauri.

The Dutch astronomer Pieter Oosterhoff noticed that there appear to be two populations of globular clusters, which became known as Oosterhoff groups. The second group has a slightly longer period of RR Lyrae variable stars. Both groups have weak lines of metallic elements. But the lines in the stars of Oosterhoff type I (OoI) cluster are not quite as weak as those in type II (OoII). Hence type I are referred to as "metal-rich" (for example, Terzan 7), while type II are "metal-poor."

These two populations have been observed in many galaxies, especially massive elliptical galaxies. Both groups are nearly as old as the universe itself and are of similar ages, but differ in their metal abundances. Many scenarios have been suggested to explain these subpopulations, including violent gas-rich galaxy mergers, the accretion of dwarf galaxies, and multiple phases of star formation in a single galaxy. In the Milky Way, the metal-poor clusters are associated with the halo and the metal-rich clusters with the bulge.

In the Milky Way it has been discovered that the large majority of the low metallicity clusters are aligned along a plane in the outer part of the galaxy's halo. This result argues in favor of the view that type II clusters in the galaxy were captured from a satellite galaxy, rather than being the oldest members of the Milky Way's globular cluster system as had been previously thought. The difference between the two cluster types would then be explained by a time delay between when the two galaxies formed their cluster systems.>>
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Re: Hubble Finds Relic Galaxy Close to Home

Post by Ann » Wed Mar 14, 2018 2:27 am

neufer wrote:
Tue Mar 13, 2018 3:48 am

https://en.wikipedia.org/wiki/Globular_cluster wrote:
<<Globular clusters are generally composed of hundreds of thousands of low-metal, old stars. Some globular clusters, like Omega Centauri in the Milky Way and G1 in M31, are extraordinarily massive, with several million solar masses and multiple stellar populations. Both can be regarded as evidence that supermassive globular clusters are in fact the cores of dwarf galaxies that are consumed by the larger galaxies. About a quarter of the globular cluster population in the Milky Way may have been accreted along with their host dwarf galaxy.

Globular clusters normally consist of Population II stars, which have a low proportion of elements other than hydrogen and helium when compared to Population I stars such as the Sun.
Click to play embedded YouTube video.
:arrow: Terzan 5 has one of the highest metallicities among the Milky Way's globular clusters—[Fe/H]=−0.21. In 2009 it was discovered that Terzan 5 consists of at least two generations of stars with ages of 12 and 4.5 billion years and slightly different metallicities, possibly indicating that it is the core of a disrupted dwarf galaxy, not a true globular cluster. There are only a few other globular clusters in the Milky Way that contain stars with different ages. Among them are M54 and Omega Centauri.

The Dutch astronomer Pieter Oosterhoff noticed that there appear to be two populations of globular clusters, which became known as Oosterhoff groups. The second group has a slightly longer period of RR Lyrae variable stars. Both groups have weak lines of metallic elements. But the lines in the stars of Oosterhoff type I (OoI) cluster are not quite as weak as those in type II (OoII). Hence type I are referred to as "metal-rich" (for example, Terzan 7), while type II are "metal-poor."

These two populations have been observed in many galaxies, especially massive elliptical galaxies. Both groups are nearly as old as the universe itself and are of similar ages, but differ in their metal abundances. Many scenarios have been suggested to explain these subpopulations, including violent gas-rich galaxy mergers, the accretion of dwarf galaxies, and multiple phases of star formation in a single galaxy. In the Milky Way, the metal-poor clusters are associated with the halo and the metal-rich clusters with the bulge.

In the Milky Way it has been discovered that the large majority of the low metallicity clusters are aligned along a plane in the outer part of the galaxy's halo. This result argues in favor of the view that type II clusters in the galaxy were captured from a satellite galaxy, rather than being the oldest members of the Milky Way's globular cluster system as had been previously thought. The difference between the two cluster types would then be explained by a time delay between when the two galaxies formed their cluster systems.>>
Correct me if I am wrong, but I'm still getting the impression that most of the Milky Way's globular clusters are very metal-poor. Are most of them aligned along a plane in the outer part of our galaxy's halo? Does that imply that most of them were stolen from satellite galaxies?

Doesn't that mean that most globulars were made by tiny satellite galaxies, not by larger galaxies like the Milky Way (which must have started out pretty small itself)?

So the Milky Way stole most of its globulars from satellite galaxies and ate the small satellite galaxies that made the globulars?

But NGC 1277 didn't steal any globulars, but made all of them itself? And we can tell that the globulars of NGC 1277 weren't stolen because they are all pretty metal-rich?

I still find this confusing.

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Re: Hubble Finds Relic Galaxy Close to Home

Post by neufer » Wed Mar 14, 2018 3:08 am

Ann wrote:
Wed Mar 14, 2018 2:27 am

I still find this confusing.
It is confusing and understood imperfectly.

Look what has be found out about NGC 1277's supermassive black hole if you want "clarity":
https://en.wikipedia.org/wiki/NGC_1277 wrote:
<<Initial studies of NGC 1277 detected the possible presence of a supermassive black hole at the center of this galaxy.

Observations made using the Hobby-Eberly Telescope at Texas's McDonald Observatory, suggested the presence of a black hole with a mass of about 1.7×1010 M (17 billion solar masses), equivalent to 14% of the total stellar mass of the galaxy due to the motions of the stars near the center of the galaxy. This makes the black hole in NGC 1277 one of the largest known, in relation to the mass of its host galaxy.

A follow up study, based on the same data and published the following year, reached a very different conclusion. The black hole that was initially suggested at 1.7×1010 M was not particularly over massive. The black hole was estimated to be between 2 and 5 billion solar masses. This is about less than a third of the previously estimated mass which is significantly lower. Models with no black hole at all were found to provide reasonably good fits to the data, including the central region. Nevertheless, it still remains as one of the most massive black holes ever discovered, at 29.6 billion kilometers in diameter – almost five times the distance from the Sun to Pluto.

Recent studies have been conducted using adaptive optics to acquire a better estimate of the mass of the black hole.

A group made observations used Gemini Near infrared Integral Field Spectrometer to better determine the mass of the black hole at the center of NGC 1277. The group used similar models to that of van den Bosch but with higher resolution. After using stellar dynamics and luminosity models to estimate the mass of the black hole they came to a mass of 4.9×109 M similar to the follow up study done by Emsellem which estimated a mass between 2–5 billion solar masses. With this mass NGC 1277 still contains one of the most massive black holes but whether it is still considered a supermassive black hole is still to be determined.

More recently a group made observations using the Keck I Telescope and a black hole with mass 1.2×109 M fit the models the best. This value agrees with the studies done by Walsh and Emsellem though it is still four times smaller than reported and is one order of magnitude smaller than first reported by van den Bosch.>>
:roll:
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Re: Hubble Finds Relic Galaxy Close to Home

Post by Ann » Wed Mar 14, 2018 7:07 am

neufer wrote:
Wed Mar 14, 2018 3:08 am
Ann wrote:
Wed Mar 14, 2018 2:27 am

I still find this confusing.
It is confusing and understood imperfectly.

Look what has be found out about NGC 1277's supermassive black hole if you want "clarity":
https://en.wikipedia.org/wiki/NGC_1277 wrote:
<<Initial studies of NGC 1277 detected the possible presence of a supermassive black hole at the center of this galaxy.

Observations made using the Hobby-Eberly Telescope at Texas's McDonald Observatory, suggested the presence of a black hole with a mass of about 1.7×1010 M (17 billion solar masses), equivalent to 14% of the total stellar mass of the galaxy due to the motions of the stars near the center of the galaxy. This makes the black hole in NGC 1277 one of the largest known, in relation to the mass of its host galaxy.

A follow up study, based on the same data and published the following year, reached a very different conclusion. The black hole that was initially suggested at 1.7×1010 M was not particularly over massive. The black hole was estimated to be between 2 and 5 billion solar masses. This is about less than a third of the previously estimated mass which is significantly lower. Models with no black hole at all were found to provide reasonably good fits to the data, including the central region. Nevertheless, it still remains as one of the most massive black holes ever discovered, at 29.6 billion kilometers in diameter – almost five times the distance from the Sun to Pluto.

Recent studies have been conducted using adaptive optics to acquire a better estimate of the mass of the black hole.

A group made observations used Gemini Near infrared Integral Field Spectrometer to better determine the mass of the black hole at the center of NGC 1277. The group used similar models to that of van den Bosch but with higher resolution. After using stellar dynamics and luminosity models to estimate the mass of the black hole they came to a mass of 4.9×109 M similar to the follow up study done by Emsellem which estimated a mass between 2–5 billion solar masses. With this mass NGC 1277 still contains one of the most massive black holes but whether it is still considered a supermassive black hole is still to be determined.

More recently a group made observations using the Keck I Telescope and a black hole with mass 1.2×109 M fit the models the best. This value agrees with the studies done by Walsh and Emsellem though it is still four times smaller than reported and is one order of magnitude smaller than first reported by van den Bosch.>>
:roll:
Confusing indeed.

Does NGC 1277 have a whopping black hole, a mid-sized black hole, a small black hole or no black hole at all? All alternatives seem possible!

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Re: Hubble Finds Relic Galaxy Close to Home

Post by Ann » Thu Mar 15, 2018 12:38 am

The Perseus Cluster. Smallish horizontally elongated
galaxy NGC 1277 is at about 10 o'clock.
Credit & Copyright: Jean-Charles Cuillandre (CFHT) & Giovanni Anselmi
(Coelum Astronomia), Hawaiian Starlight
An important aspect of NGC 1277 is that it is a member of the huge Perseus Cluster of galaxies. I believe that such an environment is extremely metal-rich.

NGC 1277 is probably about the same size as the Milky Way, but there are galaxies in the Perseus Cluster that are much bigger. I would guess that NGC 1277 formed under quite different circumstances than the Milky Way. For one thing, there may not have been many low-metallicity dwarf galaxies around where and when NGC 1277 formed. And if there were any such pristine star cities around, these low-metal morsels and their globulars may have been swallowed by bigger bullies in the neighborhood than NGC 1277.

So the smorgasboard of external low-metallicity globulars that were around for the Milky Way to help itself to may have been missing in the galactic neighbor hood where NGC 1277 had its formative years.

And maybe, just maybe, the various strong gravitational fields of a dense group of galaxies may make the orbits of the stars inside one of the lesser galaxies behave strangely - apropos the conflicting ideas of the size of the black hole inside NGC 1277.

Ann
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