(Not fully alliterative, but it’s the best I can do after driving 6 hours today.)

The halos of galaxies are best known for harboring dark matter, but they also contain stars. Only a tiny fraction of the total stars in a galaxy are in the halo, so usually they’re hard to spot, but astronomers are realizing they can contribute a significant amount to the total light profile. In particular, a group of researchers using the Spitzer infrared space telescope has determined that much of the infrared haze in the sky is due to galaxies that formed in the early Universe—including their halo stars.

However, the earliest stars and galaxies should contribute to the total infrared glow of the Universe, known as the cosmic near-infrared background (CNIB). (“Near-infrared” refers to wavelengths closest to visible light in the electromagnetic spectrum; in this case, the study was in the 1 to 5 micron range.) Much of the haze in the CNIB is from the Milky Way and known galaxies, but a significant portion is not associated with any obvious sources. Astronomers have postulated it must originate in either to dwarf galaxies (which are too small to be seen at significant distances) or faint galaxies from the early Universe. [Read more….]

Halo star haze helps hidden galaxies look huge

Since 1995, a team of astronomers led by Andrea Ghez has been studying the motion of stars near the center of the Milky Way. They just announced the discovery that one of those stars is the closest to the black hole yet, with an orbital period of about 11.5 years—short enough that they’ve been able to track its entire orbit. This could be good news for testing general relativity in a new regime of strong gravity.

One of the earliest identified S-stars was S0-2, with an orbital period of about 16 years. Until the discovery of S0-102, it was the only star with a sufficiently short orbital period to enable a complete three-dimensional reconstruction of its trajectory, which provided the best data on the shape of the black hole’s gravitational influence. [Read more….]

Animation of star motion near the central black hole, based on real infrared observations. [Credit: Andrea Ghez et al./UCLA/Keck]

The darkness at the center of the galaxy