Tidal tails detected around a distant globular cluster

May 22, 2017 by Tomasz Nowakowski, Phys.org report

Left: Number density of galaxies around the NGC 7492 globular cluster. Right: E(B − V ) extinction around the cluster. Credit: Navarrete et al., 2017.
(Phys.org)—Astronomers have found tidal tails around a distant globular cluster known as NGC 7492. The newly discovered features could provide important information about the nature of globular clusters. The findings were presented in a paper published May. 11 on the arXiv preprint repository.

Tidal tails are thin, elongated regions of stars and interstellar gas extending into space. They are formed as a result of gravitational interactions between galaxies and star clusters. Studying tidal tails offers clues on the tides experienced by the and its internal dynamics. Such studies can also reveal essential information about the evolution of a cluster and could shed new light on the lumpiness of dark matter distribution in a galaxy.

To date, only a handful of clusters with tidal tails have been detected in the Milky Way galaxy. Seeking more examples of such clusters, a team of researchers led by Camila Navarrete of the Pontifical Catholic University of Chile searched for the presence of stellar tails around located within the footprint of the Pan-STARRS1 (PS1) 3Pi survey. The survey offers multi-band, multi-epoch, precise photometry across much of the sky.

By analyzing the data provided by the first telescope of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) program, located on Haleakala, Maui, Hawaii, the team found that a globular cluster, designated NGC 7492, has the features they were looking for. Located some 86,000 light years away from the Earth, NGC 7492 is a sparse outer-halo galactic globular cluster discovered by William Herschel in 1786. The presence of extra-tidal stellar material was suggested by previous studies and has been recently confirmed by Navarrete's team.

"We report the discovery of tidal tails around the galactic globular cluster NGC 7492, based on the Data Release 1 of the Pan-STARRS 1 survey," the astronomers wrote in the paper.

According to the study, NGC 7492 exhibits two tidal tails on either side of the cluster. These features extend in the north-south direction over approximately 3.5 degrees, which corresponds to about 4,900 light years in projected length. The authors noted that the newly detected structure resembles the characteristic "S-shaped" tidal feature found around other disrupting globular clusters, like Pal 5 and NGC 5466.

Pan-STARRS observations also revealed the positions of Blue Horizontal Branch (BHB) candidate stars in the cluster. The team found that despite their overall low number density, BHBs appear to follow NGC 7492's Northern , connecting its uppermost tip with the cluster itself. However, there is an observable lack of the BHB candidates on the other side of the cluster.

"This perhaps is not surprising, given the low number of BHB stars expected in a given stellar population. While the spatial distribution of the possible BHB candidates is suggestive, deeper wide imaging is required to confirm (and perhaps extend) the discovery presented here," the team concluded.

Explore further: Two of Milky Way's globular clusters found to have halo stars

More information: The discovery of tidal tails around the globular cluster NGC 7492 with Pan-STARRS1, arXiv:1705.04324 [astro-ph.GA] arxiv.org/abs/1705.04324

Abstract
We report the discovery of tidal tails around the Galactic globular cluster NGC 7492, based on the Data Release 1 of the Pan-STARRS 1 survey. The tails were detected with a version of the matched filter technique applied to the (g−r,r) and (g−i,i) color-magnitude diagrams. Tidal tails emerging from the cluster extend at least ∼3.5 degrees in the North-East to South-East direction, equivalent to ∼1.5 kpc in projected length.

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11 comments

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Tuxford
1.8 / 5 (10) May 22, 2017
NGC 7492 exhibits two tidal tails on either side of the cluster.

A telling clue that the intermediate core star in the center of the cluster is ejecting new matter via polar jets as in supermassive core stars.

Just further confirmation that cluster is growing, from new matter generated from within the core, rather than from fanciful merger scenarios.

And it is further confirmation that the cluster is likely on the move, eventually to depart the host galaxy and form a new galaxy itself. This is the way galactic clusters form.
HannesAlfven
1.5 / 5 (8) May 22, 2017
LOL on the double tidal tail! Great catch, Tuxford.

Re: "Tidal tails are thin, elongated regions of stars and interstellar gas extending into space. They are formed as a result of gravitational interactions between galaxies and star clusters."

This is really the worst kind of science journalism. Science journalists should know enough about the context that they can themselves distinguish a conjecture from an observation. This journalist obviously lacks exposure to the Halton Arp debate and would seem to not understand that filaments are rather common in the plasma laboratory.
RNP
4.6 / 5 (9) May 23, 2017
@HannesAlfven
This is really the worst kind of science journalism. Science journalists should know enough about the context that they can themselves distinguish a conjecture from an observation. This journalist obviously lacks exposure to the Halton Arp debate and would seem to not understand that filaments are rather common in the plasma laboratory.


Your's is really the worst kind of opinionated, scientific ignorance. The is no "conjecture" involved. Double tidal tails arise from simple Newtonian physics and are observed in innumerable astronomical objects. See https://arxiv.org.../0702353 for a detailed description. To put it succinctly, galaxies or globular clusters orbiting larger galaxies *must* form tidal tails in both directions for the same reason that there are 2 tides a day on Earth (you can look it up if you don't already know).

I really would suggest you check your facts before posting in future.
RealityCheck
2 / 5 (4) May 26, 2017
@RNP.
@HannesAlfven
..and would seem to not understand that filaments are rather common in the plasma laboratory.
...galaxies or globular clusters orbiting larger galaxies *must* form tidal tails in both directions for the same reason that there are 2 tides a day on Earth..
Can you justify your assertion there, RNP? I only ask because, as far as I understand the 'two-tides per day' on Earth, it is because the Earth 'spins'; so that 'centrifugal effect' creates the 'tidal bulge' on side opposite to Moon's position. In other words, if the Earth did NOT 'spin' there would be 'only one tide' always facing Moon as it orbits Earth.

The point being: Unless the stellar globular cluster of the above article is 'spinning', your 'explanation' for its 'two tails' as being....
..for the same reason that there are 2 tides a day on Earth..
....is non-sequitur.

Can you see what I mean, RNP? If so, you'll need to offer HA another 'explanation' for them. Ok?
Captain Stumpy
5 / 5 (3) May 26, 2017
@idiot pseudoscience crackpot & delusional fraudulent liar with a police record
In other words, if the Earth did NOT 'spin' there would be 'only one tide' always facing Moon as it orbits Earth.
I really would suggest you check your facts before posting in future

1- Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun and the rotation of the Earth (see wiki for a simplified explanation since you can't be bothered to learn from any other source but your own delusional beliefs)

2- https://en.wikipe...view.svg

3- if ya can't comprehend the basics, you really should STFU and learn

4- 6,758 posts and still counting
RealityCheck
2.6 / 5 (5) May 27, 2017
@Captain Stumpy.

Please leave out the hatred, mate. Then think in context. RNP referred to the 'two-tides-a-day' case: that can only be due to ONE body apart from Earth (ie, the Moon). If we include the SUN as well it is more complicated (the 'bulges' are not 'simple form' but 'extended/flatttened'). Hence why the 'TWO-tides-per-day' case I mentioned using only the Moon AND Earth SPIN information for simplicity.

The point: EVEN IF we also include the Sun, it is still the EARTH's SPIN that creates the OTHER BULGE on the OTHER side furthest from SUN. Ok?

So you see, Stumpy, the TWO 'tidal bulges' are due to EARTH's SPIN. Ok?

So UNLESS the above globular cluster is SPINNING, then RNP's 'explanation' as offered to HA is non-sequitur/inapplicable. Ok?

PS: Stumpy, please forget your personal feuds and stick to the context/issue as presented in discussion. Thanks. :)
Captain Stumpy
4 / 5 (4) May 27, 2017
@idiot pseudoscience crackpot & delusional fraudulent liar with a police record
Please leave out the hatred, mate. Then think in context
1- there is no hate

2- it was taken in context

3- considering i've posted more information that is factual than all your posts above, and all of it can be validated with a simple search, you have no right to ask for any concessions

especially considering

4- 6,759 posts and still counting

PS: idiot pseudoscience crackpot & delusional fraudulent liar with a police record, please forget your personal feuds and stick to the context/issue as presented in discussion while presenting links and references or STFU. reported. Thanks

PPS: don't bother expecting anything but a reported post unless you provide links and references from reputable peer reviewed sources supporting you
RealityCheck
2 / 5 (4) May 27, 2017
@Captain Stumpy.
@idiot pseudoscience crackpot & delusional fraudulent liar with a police record
Please leave out the hatred,
there is no hate
Stumpy, your address line is 'dripping with hate'. So you just lied again. It is also a a lie re "police record"; since you/ZergSurfer found NO "police record" (you won't because I haven't one). So please retract; else be a demonstrable liar/malicious internet troll, Stumpy.
Then think in context
it was taken in context
But you missed the point/context re SPIN aspect. Do you NOW understand the relevance of that aspect, Stumpy; as a non-sequitur in RNP's argument to HA?
Stumpy, please forget your personal feuds; stick to context/issue as presented in discussion.
considering i've posted more information that is factual ....no right to ask for any concessions
You posted non-sequiturs/lies, from the very opening address line, Stumpy. And Stumpy, it's Scientific Method demands Objectivity/Relevance, ok? :)
Captain Stumpy
5 / 5 (1) May 29, 2017
@idiot pseudoscience crackpot & delusional fraudulent liar with a police record
blah blah blah bullsh*t blah stupidity repeated lies and fraudulent claims

And Stumpy, it's Scientific Method demands Objectivity/Relevance
it also requires evidence to validate a claim

and to date you've posted 6,770 times without being able to provide the evidence you claimed

that number isn't arbitrarily picked from a hat
it is a carefully tracked and recorded number based upon research and it can be validated by anyone who goes through your posting history

so that makes you not only the biggest liar here, but also a demonstrable chronic liar

if i am lying you should be able to refute it with evidence

So please retract your BICEP and other BS claims; else be a demonstrable liar/malicious internet troll

reported for being a liar and fraud, ok? :)
FOAD
Da Schneib
4 / 5 (4) May 29, 2017
The morphology of globular clusters is an important datum as input to galaxy formation and evolution models.

It's predictable that the mathematically challenged who are incapable of understanding the models would whine about it. It's amusing to see the #deniers take the bait.
RealityCheck
2.3 / 5 (3) May 29, 2017
@Captain Stumpy.
@idiot pseudoscience crackpot & delusional fraudulent liar with a police record
Tell the forum again that your posts aren't driven by hate, Stumpy. The address lines of your posts drip with both hate and lies, Stumpy. Even your 'mates' can see this truth which you keep denying to yourself. It's not healthy for your psyche, Stumpy, to post lies and hatred filled rants. Please stop before your mates disown you altogether because you are shaming even them by association with you and your unconscionable internet behavior. Please stop it, Stumpy; for your own sake, mate. Ok?
it also requires evidence to validate a claim
You just lied about me having a "police record", without a shred of evidence (because I haven't one; and you know it, don't you, Stumpy?). Even ZergSurfer found no police record (he only found incidental indications of my science/tech inventions/work). Which raises the question: Why would you lie about a thing like that, Stumpy? Sad.

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