HOAG’S OBJECT; TALE OF A RING GALAXY

IDL TIFF file

Image Credit & Copyright: NASA/ESA Hubble Space Telescope.

Here’s an oldie but a goodie as well as an amazing example of how detective work is crucially important in the field of astronomy. This is a Hubble Space Telescope image of the unusual yet beautiful galaxy known as Hoag’s Object which is named after Arthur Allen Hoag who discovered this object in 1950.  It’s what’s known as a ring galaxy and it’s located in the constellation Serpens a whopping (have a seat for this one) 600 million light years away.  Go ahead and think about that for a while and blow your own mind.

What causes galaxies to form like this? The real answer is that nobody knows as of yet.  The going hypothesis is that it has either undergone a collision or near miss with another galaxy as they passed by one another some two to three billion years ago.  The ring of stars may have even been captured by this galaxy, we’re simply unsure.  One thing is certain however.  The ring of stars is full of fairly new bright blue stars while the nucleus is in stark contrast.  That region is dominated by the telltale sign of ancient yellow stars which is a fairly common feature in most galaxies.  Astronomers are also unsure if that gap is in fact a gap or if it’s laced with a faint layer of stars or star clusters.

As rare as these objects are, amazingly if you look just inside the blue ring at about the 1 o’clock position you will see, millions of light years beyond, yet another ring galaxy bearing a striking resemblance to this one.

NAME: Hoag’s Object, PGC 54559.

WHAT IS IT?: Ring Galaxy.

HOW FAR AWAY IS IT?: 600 million light years (180 million parsecs).

HOW BIG IS IT?: Roughly 120 light years in diameter.

APPARENT MAGNITUDE?: Almost not worth discussing at 16.

WHERE IS IT? (General): Constellation Serpens.

WHERE IS IT? (Exact RA/DEC J2000): R.A. 15h 17m 15s / Dec. +21° 35′ 07″.

Hubblesite News Release page for this image: http://hubblesite.org/newscenter/archive/releases/2002/21/image/a/

Hubble Heritage release of this image: http://heritage.stsci.edu/2002/21/

The Astrophysical Journal; Structure & Evolution of Hoag’s Object: http://hubblesite.org/pubinfo/pdf/2002/21/rel/ApJ320-454-1987.pdf

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2 Responses to HOAG’S OBJECT; TALE OF A RING GALAXY

  1. How do you know it’s not an Einstein ring?

    • AstroDan77 says:

      Great question but there are quite a few reasons that we know it’s not that.
      1) The ring structure isn’t distorted at all. It’s arms are clear as we can observe them like any other galaxy.
      2) The ring structure is much wider than we see in the thinly stretched bands of lensed objects.
      3) Most importantly, the ring and the central object are the same distance away with the same red shift. Had this been lensing the ring would have be me much much further and thus much more red shifted than the central object for that central object to be able to curve its light around.

      Thanks again!

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