Dragan
March 31st, 2013, 04:17 PM
M87 - Galaxy
Virgo
12 30 49.7
12 23 24
Mag: 8.3
M87? Really? Yes really!
This weeks OOTW isn’t just about M87 itself. It is about a little known group of objects that M87 represents. Deep within M87 lays an object that is still quite mysterious to astronomers. A true monster if you will.
M87 harbors a DRAGN (http://www.jb.man.ac.uk/atlas/dragns.html) or a Double Radio Source Associated with a Galactic Nucleus. Much is still being learned about DRAGNs such as what exactly constitutes one, how many are there and how they are formed. There does seem to be a few criteria that are required for a DRAGN to be recognized, such as:
DRAGNs are exclusively associated with elliptical galaxies.
Most are associated with extremely large black holes some of which are on the order of millions of solar masses.
DRAGNs will always have 2 opposing lobes as well as 2 opposing jets. The lobes will contain no more than "2 hotspots" (see image below)
Interestingly these jets, such as those in the quasar 3c405 (Cygnus A), are believed to be traveling at large percentages the speed of light! One more tidbit, DRAGNs can vary in size from the smallest being approximately 30 light years across to the largest being true behemoths at over 6 million lys across, vastly larger than its host galaxy!
Unfortunately, the lobes and jets that comprise a DRAGN are typically invisible to us visual observers. After all, they are radio sources and lie deep withing giant ellipticals. But I bring to you this list more for the mental gymnastics that is associated with such an exotic object. As you observe the DRAGN catalog, know that you’re looking at objects that are true monsters! The radio images here (http://www.cv.nrao.edu/~abridle/images.htm) are breathtaking, especially the stacked images that have both radio and optical imagery superimposed on each other. They give a good representation of just how large these objects are relative to their host galaxy!
The list of known DRAGNs contain 85 different objects, 55 of which are dimmer than 16th magnitude. Save those for the most ideal of conditions! ;) 15 objects on the list are in the 13 – 16th magnitude range and the remaining 15 objects are brighter than 13th mag. Of this last group, several are well known. M84, NGC 383, NGC 1275 and NGC 6166 are all DRAGNs. But the title for “Most Famous DRAGN” has to be given to M87.
M87 is a type E+0-1 pec galaxy in Virgo. The jet of M87, which has been a deep sky challenge for as long as I can remember and is practically on every challenge list you receive at spring starparties, is typically reserved for the best of conditions. Little did I know the night I first observed the jet that it was only one half of a DRAGN. And if the jet wasn’t enough to challenge your skills and equipment, M87 holds even more challenges. UGC 7652, a 16.4 mag glow and 16.0th magnitude MAC 1230+1221 both of which are background galaxies seen through the halo of M87. (UGC7652 lies in between M87 and the MAC) Which have you seen? Here’s a tip to remember, don’t make the mistake I did the first time thinking the UGC is the jet. It’s not!
The list of DRAGNs and their host galaxies will make a good novelty challenge for any observer. Some are relatively bright at 9th mag. Others will be impossible at 20+! But for the ones we can see, it is just really incredible to know that something truly unique is going on in the cores of these galaxies.
So download the list here (http://www.jb.man.ac.uk/atlas/optical.html) and add them to your list of targets. Some objects will be old friends and others may be new.
543
(HST jet image)
544
545
Typical DRAGN
And as always:
“Give it a go and let us know!
Good luck and great viewing!”
Virgo
12 30 49.7
12 23 24
Mag: 8.3
M87? Really? Yes really!
This weeks OOTW isn’t just about M87 itself. It is about a little known group of objects that M87 represents. Deep within M87 lays an object that is still quite mysterious to astronomers. A true monster if you will.
M87 harbors a DRAGN (http://www.jb.man.ac.uk/atlas/dragns.html) or a Double Radio Source Associated with a Galactic Nucleus. Much is still being learned about DRAGNs such as what exactly constitutes one, how many are there and how they are formed. There does seem to be a few criteria that are required for a DRAGN to be recognized, such as:
DRAGNs are exclusively associated with elliptical galaxies.
Most are associated with extremely large black holes some of which are on the order of millions of solar masses.
DRAGNs will always have 2 opposing lobes as well as 2 opposing jets. The lobes will contain no more than "2 hotspots" (see image below)
Interestingly these jets, such as those in the quasar 3c405 (Cygnus A), are believed to be traveling at large percentages the speed of light! One more tidbit, DRAGNs can vary in size from the smallest being approximately 30 light years across to the largest being true behemoths at over 6 million lys across, vastly larger than its host galaxy!
Unfortunately, the lobes and jets that comprise a DRAGN are typically invisible to us visual observers. After all, they are radio sources and lie deep withing giant ellipticals. But I bring to you this list more for the mental gymnastics that is associated with such an exotic object. As you observe the DRAGN catalog, know that you’re looking at objects that are true monsters! The radio images here (http://www.cv.nrao.edu/~abridle/images.htm) are breathtaking, especially the stacked images that have both radio and optical imagery superimposed on each other. They give a good representation of just how large these objects are relative to their host galaxy!
The list of known DRAGNs contain 85 different objects, 55 of which are dimmer than 16th magnitude. Save those for the most ideal of conditions! ;) 15 objects on the list are in the 13 – 16th magnitude range and the remaining 15 objects are brighter than 13th mag. Of this last group, several are well known. M84, NGC 383, NGC 1275 and NGC 6166 are all DRAGNs. But the title for “Most Famous DRAGN” has to be given to M87.
M87 is a type E+0-1 pec galaxy in Virgo. The jet of M87, which has been a deep sky challenge for as long as I can remember and is practically on every challenge list you receive at spring starparties, is typically reserved for the best of conditions. Little did I know the night I first observed the jet that it was only one half of a DRAGN. And if the jet wasn’t enough to challenge your skills and equipment, M87 holds even more challenges. UGC 7652, a 16.4 mag glow and 16.0th magnitude MAC 1230+1221 both of which are background galaxies seen through the halo of M87. (UGC7652 lies in between M87 and the MAC) Which have you seen? Here’s a tip to remember, don’t make the mistake I did the first time thinking the UGC is the jet. It’s not!
The list of DRAGNs and their host galaxies will make a good novelty challenge for any observer. Some are relatively bright at 9th mag. Others will be impossible at 20+! But for the ones we can see, it is just really incredible to know that something truly unique is going on in the cores of these galaxies.
So download the list here (http://www.jb.man.ac.uk/atlas/optical.html) and add them to your list of targets. Some objects will be old friends and others may be new.
543
(HST jet image)
544
545
Typical DRAGN
And as always:
“Give it a go and let us know!
Good luck and great viewing!”