Wednesday, December 10, 2008

Why PhD degrees in astronomy and planetary sciences take so long

The citation below is for a preprint (accepted for publication in ApJ) which is the culmination of 16 years worth of observations.

The researchers have essentially confirmed, by examining the orbits of stars exceedingly close to the galactic center (called "S-stars," they are found within one arcsecond of the center), that a massive black hole (about 4 million suns in mass) exists in the center of our own Milky Way. The data were collected over a 16-year span using the European Southern Observatory in Chile. The near-infrared observations were "calibrated" using radioastronomy data from the VLA of known SiO masers, a topic with which I was once involved myself. Once the S-stars were related to known stars (in position and radial velocity, from the near-IR maps and/or spectroscopy of hydrogen lines in the K-band), their orbits could be deduced, and a gravitational potential could be constructed based on the way the observed stars moved. This Keplerian gravitational potential relates to the mass at the center of the galaxy via the parameters of those stellar orbits (the researchers find R0 = 8.33 +/- 0.17(stat) +/- 0.31(sys) kpc), since it is that mass which causes the stars to proceed along the paths they do.
It has been "known" (scientifically hypothesized) for several years that a black hole existed at the center of the Milky Way; these data show that, to within extraordinary statistics (for such an observation), that is indeed the case, and that it most likely is the radio emitter Sagittarius A*.
One of the researchers, Reinhard Genzel, was quoted on the BBC as saying:
"Undoubtedly the most spectacular aspect of our 16-year study, is that it has delivered what is now considered to be the best empirical evidence that super-massive black holes do really exist.... The stellar orbits in the galactic centre show that the central mass concentration of four million solar masses must be a black hole, beyond any reasonable doubt."
And I'd say that's pretty good for 16 years' worth of work.

S. Gillessen, F. Eisenhauer, S. Trippe, T. Alexander, R. Genzel, F. Martins, T. Ott (2008). Monitoring Stellar Orbits around the Massive Black Hole in the Galactic Center The Astrophysics Journal DOI: 2008arXiv0810.4674G


  1. Good stuff, I put you on my Stumble list. Maybe I'll see you over @ scienceblogs or BA. I feel lucky that my doc only took 4 years (also from a noted Colorado U)!

  2. Hey, ennui, thanks for the kind word! I do spend (I mean waste) a decent amount of time over at scienceblogs. Congrats on the 4-year-PhD!

  3. I think writing any paper, whether it is dissertation, thesis, research paper, term paper, etc can really take a lot of time, especially if you don’t know what to do. And I think the topic of the thesis writing can also be a factor adding to the time consuming writing. Anyway, even though it takes a long time to complete it, at least you can have something to call your own work.


Think carefully before you post. I reserve the right to moderate any comments posted to my blog.