by Ann » Fri Dec 26, 2014 6:10 am
The great thing about this picture is that it shows us the proximity of M77 and NGC 1055 in the sky. Are they a real pair? Are they interacting? Their radial velocities are different - compare the data from Simbad database for
M77 and
NGC 1055. But because they are certainly so relatively close to us, at about the same distance as the Virgo Cluster, their individual proper motion is large compared with their cosmic redshift, and their redshift can't reliably be used to infer the distance to them. They do look like a pair, even though I can't spot any tidal tails or any other obvious signs of interaction. But they are basically the same size, and the apparent distance between them seems quite typical for galaxies that are gravitationally bound to each other.
Both are quite dusty. Both are almost two magnitudes brighter in far infrared than in blue light, and this is indicative of a lot of dust. Dust is often associated with star formation or even with starbursts, which produce a lot of dust. There is no sign of any starburst in either of these galaxies, but an interesting possibility is that they may have undergone starbursts in the moderately recent past due to their interactions. If they have undergone recent starbursts, the hot bright stars have burned out, but the dust they left behind still remains. Of course, in the case of M77, the supermassive black hole in the center may also produce a lot of dust.
The colors of this picture are mostly pale. Certainly the galaxies look pale. The colors of galaxies are always pale, because they are made up of a mixture of stars of many colors. Even so there are color gradients and color differences in most spiral galaxies, and we can see them particularly well if the galaxy is oriented face on, like
M77. But the paleness of today's APOD is not wrong, because it underscores the typical muted hues of galaxies.
It is quite startling to see a few very colorful stars in the image. The very blue star is HD 16835 of spectral class F0. It is very much bluer than the Sun, but not nearly as blue as Vega, for example. The yellow-looking star relatively close to M77 is SAO 130073 of spectral class M0, and it is very much more yellow-orange than the Sun.
I'm not sure of the orientation of this picture. In my software, MGC 1055 is located north to northwest of M77 (that is, it is located to the upper right of M77). The blue star near NGC 1055 is located to the left (east) of the more colorless bright star near the same galaxy. The yellowish star near M77 is located to the left (east) of the galaxy in my software.
Ann
The great thing about this picture is that it shows us the proximity of M77 and NGC 1055 in the sky. Are they a real pair? Are they interacting? Their radial velocities are different - compare the data from Simbad database for [url=http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=NGC+1068&submit=SIMBAD+search]M77[/url] and [url=http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=NGC+1055&submit=SIMBAD+search]NGC 1055[/url]. But because they are certainly so relatively close to us, at about the same distance as the Virgo Cluster, their individual proper motion is large compared with their cosmic redshift, and their redshift can't reliably be used to infer the distance to them. They do look like a pair, even though I can't spot any tidal tails or any other obvious signs of interaction. But they are basically the same size, and the apparent distance between them seems quite typical for galaxies that are gravitationally bound to each other.
Both are quite dusty. Both are almost two magnitudes brighter in far infrared than in blue light, and this is indicative of a lot of dust. Dust is often associated with star formation or even with starbursts, which produce a lot of dust. There is no sign of any starburst in either of these galaxies, but an interesting possibility is that they may have undergone starbursts in the moderately recent past due to their interactions. If they have undergone recent starbursts, the hot bright stars have burned out, but the dust they left behind still remains. Of course, in the case of M77, the supermassive black hole in the center may also produce a lot of dust.
The colors of this picture are mostly pale. Certainly the galaxies look pale. The colors of galaxies are always pale, because they are made up of a mixture of stars of many colors. Even so there are color gradients and color differences in most spiral galaxies, and we can see them particularly well if the galaxy is oriented face on, like [url=http://apod.nasa.gov/apod/image/0612/M77FCRS_crawford_c.jpg]M77[/url]. But the paleness of today's APOD is not wrong, because it underscores the typical muted hues of galaxies.
It is quite startling to see a few very colorful stars in the image. The very blue star is HD 16835 of spectral class F0. It is very much bluer than the Sun, but not nearly as blue as Vega, for example. The yellow-looking star relatively close to M77 is SAO 130073 of spectral class M0, and it is very much more yellow-orange than the Sun.
I'm not sure of the orientation of this picture. In my software, MGC 1055 is located north to northwest of M77 (that is, it is located to the upper right of M77). The blue star near NGC 1055 is located to the left (east) of the more colorless bright star near the same galaxy. The yellowish star near M77 is located to the left (east) of the galaxy in my software.
Ann