Star or Galaxy?

• by CyberPaddy66

  I am not sure if this is just a star with a dust disc or a smooth galaxy with a very large centre, any thoughts?

  Posted September 30, 2017 5:38 AM

• by Budgieye moderator

  Yep! a smooth galaxy with a very large center. Galaxies are "not round", and the fuzzy patch around is much larger than the nucleus.

  A star is round, and the disc is sharper and takes more of the object, and the fuzzy part is smaller.

  a star

  http://skyserver.sdss.org/dr9/en/tools/explore/obj.asp?ra=168.05961707698413&dec=-15.520004009792052

  SkyServer software measures if an object is

  round = star

  not round (ie extended light source)= galaxy

  Posted September 30, 2017 7:20 AM

• by NGC3314 scientist

  Further - dusty disks around individual stars are much harder to see than galaxies (while we sometimes see dusty reflection nebulae in SDSS images, as far as I can tell all the protoplanetary or remnant disks around single stars are too small and faint to pick out on inspecting the SDSS images).

  Here's an offbeat comparison: https://www.spacetelescope.org/images/potw1722a/ - a star whose Hubble data, carefully processed to remove as much of the star's light as possible, revealed a galaxy almost directly behind it. It's now a standing joke that the authors of the paper on it left their internal label "vermin" on the galaxy in an image that appeared on the cover of the Astronomical Journal. The unprocessed data would show only the giant splotch of starlight across that whole frame.

  Posted October 2, 2017 2:52 PM

• by Budgieye moderator

  That is so interesting, thank you Dr Keel.

  I wonder what will happen if the red star moves in front of the quasar?

  

  http://skyserver.sdss.org/dr14/en/tools/explore/Summary.aspx?id=1237668623012331586

  Posted October 2, 2017 4:24 PM

• by CyberPaddy66

  Some very usefully information, thank you both so much it is helping me to learn more than I thought possible.

  Posted October 8, 2017 9:41 AM