APOD: The Hercules Cluster of Galaxies (2020 Nov 07)

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APOD: The Hercules Cluster of Galaxies (2020 Nov 07)

Post by APOD Robot » Sat Nov 07, 2020 5:05 am

Image The Hercules Cluster of Galaxies

Explanation: These are galaxies of the Hercules Cluster, an archipelago of island universes a mere 500 million light-years away. Also known as Abell 2151, this cluster is loaded with gas and dust rich, star-forming spiral galaxies but has relatively few elliptical galaxies, which lack gas and dust and the associated newborn stars. The colors in this deep composite image clearly show the star forming galaxies with a blue tint and galaxies with older stellar populations with a yellowish cast. The sharp picture spans about 1/2 degree across the cluster center, corresponding to over 4 million light-years at the cluster's estimated distance. Diffraction spikes around brighter foreground stars in our own Milky Way galaxy are produced by the imaging telescope's mirror support vanes. In the cosmic vista many galaxies seem to be colliding or merging while others seem distorted - clear evidence that cluster galaxies commonly interact. In fact, the Hercules Cluster itself may be seen as the result of ongoing mergers of smaller galaxy clusters and is thought to be similar to young galaxy clusters in the much more distant, early Universe.

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Re: APOD: The Hercules Cluster of Galaxies (2020 Nov 07)

Post by Ann » Sat Nov 07, 2020 7:45 am

Wow, the Hercules Cluster of Galaxies is surely the best-looking galaxy cluster for anyone who likes to seeing galaxies of various shapes and hues in close proximity!

Hercules Cluster with numbers.png
Five of the most interesting (and often interacting) galaxies
in the Hercules Cluster of Galaxies.
Let's take a look at five of the more interesting galaxies!
















1) NGC 6045 was long considered the most iconic of the Hercules Cluster galaxy members, because its shape is very striking even in low-resolution images. The juxtaposition of a true cluster member and a small foreground galaxy makes NGC 6045 look like a leg with a foot.




NGC 6050 with numbers.png
NGC 6050. Photo: ESA/Hubble.


2) NGC 6050 is the true star of the Hercules Cluster, a fantastic "triple galaxy" posing as a doublet, or maybe just one major galaxy carrying two sets of "fluff and condensations" in its arms?

Take a look at the picture at left. NGC 6050A, at left, is the major galaxy. It has a big yellow bulge and two elegant spiral arms. I have marked NGC 6050A as number "1".

Number "2" is the small galaxy apparently tangled in an arm of NGC 6050A. I don't know the name of this galaxy, but as you can see it has a bright bar and a what looks like a disk surrounding the bar.

The third galaxy, number "3" in the picture at left, is NGC 6050B. As you can see, it has a quite puny center, which consists solely of a bar no brighter than the bar of galaxy "2". Yes, but look at the big, blue and wild spiral arms of NGC 6050B!

Nameless Hercules galaxy with blue bar.png



3) This is a galaxy that I want to show you even though I don't know its name. It hasn't got an NGC or IC designation. The reason why I think it is remarkable is that James D Wray, who created the Color Atlas of Galaxies in 1988, wrote in his atlas that he had never photographed a galactic bar with so much star formation in it as in this particular galaxy. James D Wray wrote:
...extraordinary blue bar. There are practically no galaxies with bars similar to this...

In Wray's atlas, the ring of the galaxy is quite invisible. In his atlas, the galaxy looks like three almost equally bright marbles in a row, the central one yellow, the two others blue.






















4) This is the galaxy with the fantastic jet, IC 1182. This galaxy also displays a tidal feature(?) in not quite the opposite direction. To me, this jet, combined with the other feature, reminds me of giant elliptical galaxy M87. I can't believe that IC 1182 is even remotely as big or massive as M87, but even so, the fantastic jet clearly suggests that the black hole of this galaxy has recently received a healthy helping of fresh material to both swallow and spit out. Compare the picture I posted with an SDSS image of IC 1182.


5) The last galaxy pair that I wanted to show you is IC 1178 and IC 1181. None of these galaxies has any reservoir of gas or any star formation, but one or both of them is a lenticular galaxy, which means it has a disk but no gas or star formation. When two such galaxies collide, they can create almost spiral-like tidal features made up entirely of stars (and planets), but due to the lack of gas, the collision doesn't lead to any star formation at all. This is called a"dry merger".

Ann
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Re: APOD: The Hercules Cluster of Galaxies (2020 Nov 07)

Post by sillyworm 2 » Sat Nov 07, 2020 12:55 pm

Thanks Ann! My favorite subject..Galaxies.Not good with links here..but I found a site( astrophoton.com) that lists IC1182 as a merger.

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Re: APOD: The Hercules Cluster of Galaxies (2020 Nov 07)

Post by orin stepanek » Sat Nov 07, 2020 2:07 pm

Abell2151_Howard_Trottier_2020_FFTelescope1024.jpg

Lotta galaxies= more stars than grains of sand; or something like that! :mrgreen:
💥 🌟 ✨ 💫 ⭐️
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Re: APOD: The Hercules Cluster of Galaxies (2020 Nov 07)

Post by bls0326 » Sat Nov 07, 2020 2:08 pm

So much slo-o-o-w motion activity!

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KNOTS!!

Post by neufer » Sat Nov 07, 2020 3:03 pm

Ann wrote:
Sat Nov 07, 2020 7:45 am

4) This is the galaxy with the fantastic jet, IC 1182. This galaxy also displays a tidal feature(?) in not quite the opposite direction. To me, this jet, combined with the other feature, reminds me of giant elliptical galaxy M87. I can't believe that IC 1182 is even remotely as big or massive as M87, but even so, the fantastic jet clearly suggests that the black hole of this galaxy has recently received a healthy helping of fresh material to both swallow and spit out. Compare the picture I posted with an SDSS image of IC 1182.
http://www.astrophoton.com/IC1182.htm wrote: IC 1182 - A Member of Abell 2151

<<IC 1182 is well known as a peculiar galaxy because of its eastwards directed tail with blue knots (size 1.3' - 200,000 Ly).

:arrow: The inverted image shows a faint second tail towards the NW.

The second fainter tail was reported by Moles et al 2004 for the first time and can be detected with only 4" aperture!

The image below was published in year 2004 in Astronomy & Astrophysics. Moles et al 2004 concluded that IC 1182 is a system of two galaxies, in the process of merging, with two tidal tails emerging from the central region of the galaxy. The knots in the main tail are developing tidal dwarf galaxies.>>
https://en.wikipedia.org/wiki/Anthony_McAuliffe wrote:
<<General Anthony Clement "Nuts" McAuliffe (July 2, 1898 – August 10, 1975) was a senior United States Army officer who earned fame as the acting commander of the U.S. 101st Airborne Division troops defending Bastogne, Belgium, during the Battle of the Bulge in World War II. He is celebrated for his one-word reply to a German surrender ultimatum: "Nuts!"

According to those present when McAuliffe received the German message, he read it, crumpled it into a ball, threw it in a wastepaper basket, and muttered, "Aw, nuts". The officers in McAuliffe's command post were trying to find suitable language for an official reply when Lt. Col. Harry Kinnard suggested that McAuliffe's first response summed up the situation pretty well, and the others agreed. The official reply was typed and delivered by Colonel Joseph Harper, commanding the 327th Glider Infantry, to the German delegation. It was as follows:
  • To the German Commander.

    "NUTS!"

    The American Commander.
The German major appeared confused and asked Harper what the message meant. Harper said, "In plain English? Go to hell."The choice of "Nuts!" rather than something earthier was typical for McAuliffe. Captain Vincent Vicari, his personal aide at the time, recalled that "General Mac was the only general I ever knew who did not use profane language. 'Nuts' was part of his normal vocabulary."

The artillery fire did not materialize, although several infantry and tank assaults were directed at the positions of the 327th Glider Infantry. In addition, the German Luftwaffe attacked the town, bombing it nightly. The 101st held off the Germans until the 4th Armored Division arrived on December 26 to provide reinforcement. >>
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Re: APOD: The Hercules Cluster of Galaxies (2020 Nov 07)

Post by ptahhotep » Sat Nov 07, 2020 4:23 pm

The group of galaxies in the bottom right corner seem to be separated from the others. Do they represent one of the smaller clusters that are merging to form the larger Hercules cluster?

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Re: APOD: The Hercules Cluster of Galaxies (2020 Nov 07)

Post by Ann » Sat Nov 07, 2020 6:54 pm

ptahhotep wrote:
Sat Nov 07, 2020 4:23 pm
The group of galaxies in the bottom right corner seem to be separated from the others. Do they represent one of the smaller clusters that are merging to form the larger Hercules cluster?
APOD Robot wrote:

In fact, the Hercules Cluster itself may be seen as the result of ongoing mergers of smaller galaxy clusters and is thought to be similar to young galaxy clusters in the much more distant, early Universe.
So yes, I find it very likely that the group of galaxies seen at bottom right is one of the smaller clusters that are in the process of merging with the larger Hercules Cluster of Galaxies.

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Re: KNOTS!!

Post by Ann » Sat Nov 07, 2020 7:37 pm

neufer wrote:
Sat Nov 07, 2020 3:03 pm
Ann wrote:
Sat Nov 07, 2020 7:45 am

4) This is the galaxy with the fantastic jet, IC 1182. This galaxy also displays a tidal feature(?) in not quite the opposite direction. To me, this jet, combined with the other feature, reminds me of giant elliptical galaxy M87. I can't believe that IC 1182 is even remotely as big or massive as M87, but even so, the fantastic jet clearly suggests that the black hole of this galaxy has recently received a healthy helping of fresh material to both swallow and spit out. Compare the picture I posted with an SDSS image of IC 1182.
http://www.astrophoton.com/IC1182.htm wrote: IC 1182 - A Member of Abell 2151

<<IC 1182 is well known as a peculiar galaxy because of its eastwards directed tail with blue knots (size 1.3' - 200,000 Ly).

:arrow: The inverted image shows a faint second tail towards the NW.

The second fainter tail was reported by Moles et al 2004 for the first time and can be detected with only 4" aperture!

The image below was published in year 2004 in Astronomy & Astrophysics. Moles et al 2004 concluded that IC 1182 is a system of two galaxies, in the process of merging, with two tidal tails emerging from the central region of the galaxy. The knots in the main tail are developing tidal dwarf galaxies.>>
IC 1182 black and white.png
Thanks, Art, very interesting. At left I have posted the picture of IC 1182 that I think that you tried to show us.
M. Molés et al. wrote about IC 1182:

There are no clear signs of nuclear activity and the observed line ratios can be explained in terms of stellar photoionization.
...
The data presented here indicate that IC 1182 is a high luminosity starburst system, involving two systems in the process of merging, with two tidal tails emerging from the central region of the galaxy.






If there are no clear signs of nuclear activity in IC 1182, then the central black hole of this galaxy is probably not acting up, and the black hole is not causing the jets.

Instead, IC 1182 is a pair of colliding galaxies, and the activity and the tidal tails are all (or mostly) caused by the tidal forces caused by the collision and the starburst that the collision initiated - very slightly similar to the Antennae galaxies, except in the Antennae we can see a bright starburst in one of the colliding galaxies, and not just in one of the tails.

Ann
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Re: APOD: The Hercules Cluster of Galaxies (2020 Nov 07)

Post by neufer » Sun Nov 08, 2020 1:37 am

APOD Robot wrote:
Sat Nov 07, 2020 5:05 am

These are galaxies of the Hercules Cluster, an archipelago of island universes a mere 500 million light-years away...In fact, the Hercules Cluster itself may be seen as the result of ongoing mergers of smaller galaxy clusters and is thought to be similar to young galaxy clusters in the much more distant, early Universe.
https://www.ligo.org/science/Publication-GW190425/index.php wrote:
<<GW190425: The heaviest binary neutron star system ever seen?

The LIGO Scientific Collaboration and Virgo Collaboration can report that, on 25th April, 2019, gravitational waves were detected from the merger of two compact objects. Our collaborations designated this signal as GW190425. LIGO comprises of two gravitational-wave detectors, one in Hanford, Washington and the other in Livingston, Louisiana. At the time of GW190425, the LIGO-Hanford detector was temporarily offline, but the strong signal was detected in the LIGO-Livingston detector. The Virgo detector, located in Cascina, Italy, was also taking data. However, due to its lower sensitivity compared to LIGO and in particular because the source of GW190425 was likely in a region of the sky less visible for Virgo, the signal was only above the detection threshold in LIGO-Livingston. Nevertheless, Virgo data were useful in helping us to understand the parameters of GW190425's source. We find the total mass of this binary to be between 3.3 and 3.7 times the mass of the Sun. Given this mass range, the most plausible explanation is that two neutron stars collided approximately 520 million light years away. The mass of this binary is significantly larger than any other known binary neutron star system.

GW190425 was detected in Advanced LIGO and Virgo's third observing run known as O3, which started on April 1st 2019 and will finish on 30th April 2020. Prior to this observing run, there have been two other observing runs with the Advanced detectors, O1 (September 2015 – January 2016) and O2 (November 2016 – August 2017), see here for more details. Between observing runs the detectors are upgraded with new technologies to increase their sensitivity.

In O2, LIGO and Virgo made the first observation of gravitational waves from the inspiral of two neutron stars, known as GW170817. This collision of neutron stars also produced a counterpart seen across the electromagnetic spectrum. GW190425 is likely our second observation of a neutron star merger with gravitational waves. To date no electromagnetic counterpart or neutrino signal has been identified in association with GW190425. This is not surprising, however, given that the source was further away than GW170817 and so the anticipated electromagnetic signal would be weaker. But perhaps the biggest factor is because GW190425 was not well localized. In fact, we localized the source of GW190425 to a region covering about 16% of the entire sky. This is a huge area of sky for conventional telescopes to search!

We have a number of searches which look for gravitational-wave signals from the merger of compact objects. They compare the observed data with theoretical signals predicted by General Relativity using a technique called matched filtering. Our search pipelines identified the GW190425 signal from the LIGO-Livingston data. The next step is to estimate how significant this event is, i.e. we want to know the rate at which we might expect such a signal to have occurred by chance due to the noise characteristics of the detector data. This quantity is known as the false alarm rate. To estimate this, we need to compare the strength of GW190425 with respect to a background distribution. A background was created by performing the search over 169.5 days of O1 and O2 and 50 days of O3, taken individually from LIGO-Livingston, LIGO-Hanford and Virgo. We found the false alarm rate for GW190425 to be one chance event in 69,000 years. Figure 2 shows that in the combined 219.5 days of background data, GW190425 clearly stands out from the background, in addition to the other confirmed detection of GW170817.

In addition to the searches, we also performed similar detection procedures on GW190425 as we have done for previous events. These checks investigate whether a rare instrumental noise transient at LIGO-Livingston could account for GW190425. We found no environmental or instrumental disturbances could account for GW190425.

We found that the mass of the heavier of the two compact objects is between 1.61 and 2.52 times the mass of the Sun, and the mass of the second object between 1.12 and 1.68 times the mass of the Sun. These masses are consistent with the masses measured from other neutron stars as well as what we might expect from supernova explosion simulations. The heaviest neutron star known from electromagnetic observations (PSR J0740+6620) is measured to be 2.05–2.24 times the mass of the Sun. For GW190425 we cannot rule out that one or both objects are black holes. However, the most straightforward interpretation is that these objects are indeed neutron stars. So, if this is the case, what can we infer about GW190425?

We find that in some ways GW190425 is not like other binary neutron stars in our Galaxy. While the mass of each neutron star is similar to those already known, the total mass is quite different. Figure 3 shows the total masses of ten galactic binary neutron star systems which are expected to merge within the lifetime of the Universe. A normal distribution has been fit to these 10 systems. We find the average galactic binary mass is about 2.69 times the mass of the Sun, while the mass of the GW190425 binary is about 3.4 times the mass of the Sun. In fact, it lies 5 standard deviations away from the Galactic mean. This suggests that GW190425 formed differently from these known Galactic binaries.

There are two ways in which we expect to form a binary with two neutron stars. One way is called the “common envelope isolated binary evolution channel”, where two neutron stars are formed when the two stars in a binary each undergo a supernova explosion but in isolation from other compact objects. The second way is called the “dynamical formation channel”. In this scenario, a binary already exists, which could contain two neutron stars or a neutron star and a main sequence star for example. Then another neutron star joins the two stars forming the binary and kicks out the lower mass star, leaving behind a binary containing two neutron stars. A dynamical origin is unlikely for GW190425 as this is not thought to contribute significantly to the merger rate of binary neutron stars. If the GW190425 binary formed in isolation, this may mean the neutron stars were born from low-metallicity stars. Or it may indicate that when the first supernova explosion happened and created the first neutron star in the binary, mass from the second star (which had not gone supernova yet) could have transferred on to the first neutron star and made it heavier. Either way, the discovery of GW190425 may suggest that there is a population of binary neutron star systems with sub-hour orbital periods which are not detectable by current electromagnetic surveys.

We also looked to see if we could tell how fast the neutron stars were rotating. Unfortunately, our results do not indicate what the spins of the neutron stars were. They are consistent with rotating like the two fastest spinning Galactic neutron star binaries that are expected to merge within the lifetime of the Universe, PSR J0737–3039A/B and PSR J1946+2052. This latter system contains a pulsar which rotates once every 17ms.

If we now take the discovery of GW190425 as a neutron star binary and combine this result with the one other binary neutron star we have observed (GW170817), we can estimate the number of neutron stars that collide in a volume of the universe every year. We find the rate of binary neutron star mergers to be between 250 and 2810 per gigaparsec cubed per year.

GW190425 is potentially the second observation of a binary neutron star, and it has given us more unique information about these strange objects.??>>
Art Neuendorffer

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Re: APOD: The Hercules Cluster of Galaxies (2020 Nov 07)

Post by Ann » Sun Nov 08, 2020 6:20 am

Tadpole Galaxy with blue knots in tail.png
Composite g, V , and I color image of UGC 10214, with a close-up of
the bright blue clump in the tail. The brightest stellar knot marked by
the red arrow is a probable super star cluster (SSC).
Parallel lines indicate the slit width and orientation used in
the Keck spectroscopy. Gerhardt Meurer/Keck Telescope.





















Speaking of the topic of colliding gas-rich galaxies with tidal tails with knotty condensations that are going to turn into dwarf galaxies, a nice example is the long tail of the Tadpole galaxy, UGC 10214.

Of course, a very well-known example of a cosmic train wreck is the sound and fury and the star formation and tidal tails of Stephan's Quintet. In the picture at right, the shock front of the collision is glowing blue in X-rays.

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Re: APOD: The Hercules Cluster of Galaxies (2020 Nov 07)

Post by starsurfer » Sun Nov 08, 2020 11:23 pm

I love the framing of this to include some of the more peculiar members on the outskirts. This is my favourite galaxy cluster and in fact it contains four entries in the Arp Atlas of peculiar galaxies.