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Deep Hubble View of Unusual “Fluffy” Galaxy – and Beyond

by Nancy Atkinson on February 5, 2009

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This deep image taken with the NASA/ESA Hubble Space Telescope shows the spiral galaxy NGC 4921 along with a spectacular backdrop of more distant galaxies. It was created from a total of 80 separate pictures taken with yellow and near-infrared filters. Credits: NASA, ESA and K. Cook (Lawrence Livermore National Laboratory, USA)

This deep image taken with the NASA/ESA Hubble Space Telescope shows the spiral galaxy NGC 4921 along with a spectacular backdrop of more distant galaxies. It was created from a total of 80 separate pictures taken with yellow and near-infrared filters. Credits: NASA, ESA and K. Cook (Lawrence Livermore National Laboratory, USA)

The Coma Galaxy cluster is home to a rich collection of galaxies in the nearby Universe. NGC 4921 is one of the rare spirals in Coma, and a rather unusual one. It looks “fluffy,” with lots of swirling dust. Astronomers say this galaxy is an “anemic spiral” where a small amount of star formation is taking place, and so less light is coming from the galaxy’s arms, as is usually seen in a spiral galaxy. This is an image from the Hubble Space Telescope, and with Hubble’s sharp vision, you can see a few bright young blue stars. But what’s really amazing, besides seeing the incredible detail of NGC 4921, is looking beyond the big fluffy galaxy and seeing how Hubble was able to pick up a marvelous collection of remote galaxies of all shapes, sizes and colors. Many have the spotty and ragged appearance of galaxies from the early Universe. Click here to get a bigger, better view.

This image was created from data obtained by Hubble’s Advanced Camera for Surveys. The Coma galaxy cluster, is in the northern constellation of Coma Berenices. The cluster, also known as Abell 1656, is about 320 million light-years from Earth and contains more than 1000 members. The brightest galaxies, including NGC 4921, were discovered back in the late 18th century by William Herschel.

Annotated deep Hubble Space Telescope image of NGC 4921 indictating the locations of some of the more interesting features of the galaxy and its surroundings. Credits: NASA, ESA and K. Cook (Lawrence Livermore National Laboratory, USA)

Annotated deep Hubble Space Telescope image of NGC 4921 indictating the locations of some of the more interesting features of the galaxy and its surroundings. Credits: NASA, ESA and K. Cook (Lawrence Livermore National Laboratory, USA)


The galaxies in rich clusters undergo many interactions and mergers that tend to gradually turn gas-rich spirals into elliptical systems without much active star formation. As a result, there are far more ellipticals and fewer spirals in the Coma Cluster than are found in quieter corners of the Universe.

The Hubble images used to make this picture were originally obtained by a team led by Kem Cook (Lawrence Livermore National Laboratory, California). The team used Hubble to search for Cepheid variable stars in NGC 4921 that could be used to measure the distance to the Coma cluster and hence the expansion rate of the Universe.

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Unfortunately the failure of the Advanced Camera for Surveys in early 2007 meant that they had insufficient data to complete their original program, although they hope to continue after the servicing mission. Very deep imaging data like this, which is available to anyone from the Hubble archives, may also be used for other interesting scientific exploration of this galaxy and its surroundings.

A wide-field image of the region around the Coma galaxy cluster (Abell 1656) constructed from the images in the Digitized Sky Survey. NGC 4921 is the largest galaxy to the left, and slightly below, the pair of galaxies at the centre of the image. The field-of-view is approximately 2.7 x 2.85 degrees. Credits: NASA, ESA, and the Digitized Sky Survey 2. Acknowledgment: Davide De Martin (ESA/Hubble)

A wide-field image of the region around the Coma galaxy cluster (Abell 1656) constructed from the images in the Digitized Sky Survey. NGC 4921 is the largest galaxy to the left, and slightly below, the pair of galaxies at the centre of the image. The field-of-view is approximately 2.7 x 2.85 degrees. Credits: NASA, ESA, and the Digitized Sky Survey 2. Acknowledgment: Davide De Martin (ESA/Hubble)


The top image was created from 50 separate exposures with a yellow filter and another 30 exposures with a near-infrared filter using the Wide Field Channel of the Advanced Camera for Surveys on Hubble. The total exposure times were approximately 17 hours and 10 hours respectively.

Source: ESA

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About

Nancy Atkinson is Universe Today's Senior Editor. She also is the host of the NASA Lunar Science Institute podcast and works with the Astronomy Cast and 365 Days of Astronomy podcasts. Nancy is also a NASA/JPL Solar System Ambassador.

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  • RapidEye

    I already made it my new desktop for the week! =-)

    I’d be curious how this would look with Spitzer and/or Chandra. Since it is “anemic” WRT star formation I’d expect to see a huge black hole signature via Chandra if current theories of black holes and how they regulate star formation is true.

    The dark areas between the arms probably don’t have a lot of dust (not much to see w/ Spitzer) because you can see background galaxies through them.

    What a great time to be in Astronomy!!! =-)

  • Procyon

    This is truly spectacular!

    Imagine all the life out there.

  • Salacious B. Crumb

    Salacious B. Crumb Says:
    February 5th, 2009 at 8:32 am e
    Holy Toledo, boy there is a awful lot of galaxies in this image… NGC 4921 certainly is fluffy galaxy wrapped in cotton wool – and is real terms is 77 Mpc (251 million light-years) from us. Also the zoomed image reveals near the centre a close near equally bright yellow double star from own galaxy. Just breathtaking.
    NASA Extragalactic Database notes on NGC 4921 says; “This is the other giant spiral in Coma, also projected close to the cluster center, at 25′ southeast (~0.5 Mpc). … it is very high H I deficiency… [and] It shows a very perturbed gas distribution, which is clearly less extended than the optical disk. Most of the H I emission is distributed along the southeast spiral arm, while the northwest appears depleted. The H I centroid exhibits a slight offset, 10″ east of the optical centre.”
    Also;
    “In NGC 4921 only little X-ray emission was detected. This emission is not concentrated at the centre of the galaxy (as would be usual for an E or S0 type system), but it is rather diffuse, with several weak emission maxima. This shallow emission distribution of NGC 4921 indicates that there is no pronounced central concentration of X-ray emitting gas, implying the absence of a cooling flow”
    This probably accounts for the odd fluffiness. Clearly it is unlike our own Milky Way.
    Certainly an inspiring image that could be inspected for hours – but don’t make it a jigsaw puzzle please…

  • Salacious B. Crumb

    RapidEye said;
    “I’d expect to see a huge black hole signature via Chandra if current theories of black holes and how they regulate star formation is true.”
    Sadly this is probably unlikely as the central region shows no real activity central concentration in the X-ray. I’d say this might be unlikely in this galaxy, but there are other candidates in the Coma Galaxy cluster that would be worth checking out.

  • http://oilismastery.blogspot.com/ OilIsMastery

    Questions:

    1. How come there is no so-called “gravitational lensing” of the remote background galaxies in that photograph?

    2. How come the alleged blackhole at the center of NGC 4921 doesn’t suck in the light of the background objects with it’s overwhelming “gravitational” force?

  • Dee

    Hubble does it again – that is absolutely stunning! I could spend all week just looking at it.

    RapidEye – you’re right. We are so lucky to be here now, when there’s so much happening and so many new things to see.

    Go Hubble! After her upgrade who knows what she will show us? Watch this space!

  • Space Cookie

    Beautiful.
    ’nuff said

  • robby

    incredible!!! I was going to crop the pic to fit the resolution of my 30″ FP, 2560×1600, but, I will lose the full perspective- so I said forget that and will hunt for the tiff image of this incredible image- so what if it requires 25-30mb of space, I can also look for hours and vegetate looking at this incredible picture lol.
    Thank you for posting this picture!!!

  • http://www.myspace.com/onekingtrain Shawn

    Can a grown man cry !?! Looking at this (magnified image) brought tears to my eyes. I can not believe the number of galaxies and space objects in this beautiful and captivating shot from Hubble. It stirs my soul! Ros den herskende Guden av universet for evig og noensinne! Flipping awesome!

  • Astrofiend

    # OilIsMastery Says:
    February 5th, 2009 at 1:30 pm

    Questions:

    1. How come there is no so-called “gravitational lensing” of the remote background galaxies in that photograph?

    2. How come the alleged blackhole at the center of NGC 4921 doesn’t suck in the light of the background objects with it’s overwhelming “gravitational” force?

    1) Look up ‘weak gravitational lensing’. Warped images, arcs and rings etc. are all firmly products of the ‘strong lensing’ regime. Strong lensing requires a VERY specific geometric relationship between viewer, lensing object and background object. Even then effects can be small unless the galaxy cluster is particularly massive. Also, it really doesn’t happen unless both source and lens are very distant – a fair bit more distant than this galaxy.

    Weak lensing is far more subtle, and is really only detectable with a huge amount of statistical analysis using many background objects. Work such as this may be happening for this image right now – who knows? So, this is all what General Relativity predicts anyway. Everything is as expected.

    2) Why would the black hole ‘suck in the light’ from the background objects? A supermassive black hole, even some of the largest, have a Schwarzchild Radius measured in tens of millions of km. That may sound a lot, but it’s only a couple of light minutes at best. So, give or take, it is about 1/ 45 billionth of the diameter of the galaxy. The original image is 3840 pixels wide, so that means that the black hole would occupy a width on the image of about 1/12 millionth of a screen pixel. Light is only sucked into a black hole if it travels on a trajectory directly into it, or starts out already inside the event horizon – i.e. the only light we would see sucked in is that which comes from directly behind it from our point of view. So, since a pixel is 2-dimensional, to get the total amount of light lost in terms of pixel area due to the black hole we take 1/(12000000^2). So a grand total of 1/144 trillionth of a pixel’s worth of light would be lost to our telescopes at this image resolution due to direct blocking by the black hole.

    Light that does not venture within the event horizon merely has it’s trajectory altered – significantly for light grazing near to the hole, but decreasing rapidly as we move further away (as the square of the distance). Now, running some (very quick and dirty) calculations with simple Newtonian gravity (fine to do in the weak field scenario we are considering), the gravity felt from the black hole would be about the same as that at the surface of the sun only about 20 light-days away from it, and the deflection of light for such a weak field is minimal to say the best – note the painstaking work required to measure the minute gravitational deflection of light by the Sun. 20 light days is still only about 1/500th of a pixel-width on the full sized image, and so there would be absolutely no visible effects in a simple colour image such as this due to the black hole. Spectroscopy however, tells us a lot more. But that is different matter entirely and another story altogether.

    Again though, everything is as expected. Gravity triumphs! Hazaaa!

  • Astrofiend

    Correction:

    “…merely has it’s trajectory altered – significantly for light grazing near to the hole, but decreasing rapidly as we move further away (as the square of the distance).”

    Should read more like “has its trajectory altered, in proportion to the strength of the gravitational well it travels through, which in the Newtonian limit goes as the inverse of the square of the distance from the hole.”

  • Astrofiend

    Also note – many of the quick and dirty calculations were based on the mass of Sgr A*. This is not a huge black hole by cosmic standards, but the points illustrated remain valid.

  • robbi

    Astrofriend-extremely well said and very understandable. It is incredible about the detail of this galaxy 320M LY away,
    Even thought I am somewhat of a computer geek like others I know on the net, the area of a pixel you mentioned verifies the enormous
    distance and what would appear to humans sense to be large entities and distances of 20 L-days, makes very clear how insigniicant 20 L-days is compared to the size of NGC 4921. Now what I hope for is to find or have NASA, ESA and K. Cook (Lawrence Livermore National Laboratory) release a TIFF image.lol

  • http://oilismastery.blogspot.com/ OilIsMastery

    Astrofiend,

    You say, “Strong lensing requires a VERY specific geometric relationship between viewer, lensing object and background object.”

    Since you are the resident expert on gravitational lenses, perhaps you can tell us what “specific geometric relationship” you refering to. What are the geometric requirements for a gravitational lens to occur?

    You say, “it really doesn’t happen unless both source and lens are very distant – a fair bit more distant than this galaxy.”

    What distance does an object need to be from the Earth in order for a gravitational lens to occur?

    You ask, “Why would the black hole ‘suck in the light’ from the background objects?”

    Great question. Since black holes don’t exist, gravity doesn’t exist, and photons are alleged to have no mass, I don’t have an answer.

    What is the mathematical relationship between mass, distance, and gravity? Why don’t so-called black holes exert gravitational force beyond the alleged Schwarzschild radius and event horizon? Why does gravity break down? At what distance from a massive object does gravity break down and what is the mathematical ratio of mass to distance in order to determine it?

    You say, “many of the quick and dirty calculations were based on the mass of Sgr A*.”

    What is the mass of Sagittarius A*? Why do stars orbit Sagittarius A* instead of falling on it by it’s gravity? At what distance from Sagittarius A* does gravity break down?

  • alphonso

    Bloody great picture!! Cool!!!!

  • pappe

    What is the object about 10% of image height below the upper right corner, looks like a globular cluster?

  • http://home.ca.inter.net/deepsky/ Rick Ellis

    Looks like a proto-galaxy in the process of acreting material. Give it a few more billion years.

  • http://home.ca.inter.net/deepsky/ RickE

    What is more impressive in the image are the myriad
    galaxies in the bg. Are we alone?

    Not a chance.

  • Timmy

    It’s the Omega Point!

  • Excalibur

    I dont think there is any point arguing with Oilsmastery, or trying to explain anything. Let him write his sarchastic comments and leave it at that, after awhile he will go away, starved from any attention – children behave like that.

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