GSFC: New Mini Satellite Will Study Milky Way's Halo

[bystander]

New Mini Satellite Will Study Milky Way's Halo
NASA | GSFC | 2018 Jul 18

Astronomers keep coming up short when they survey “normal” matter, the material that makes up galaxies, stars and planets. A new NASA-sponsored CubeSat mission called HaloSat, deployed from the International Space Station on July 13, will help scientists search for the universe’s missing matter by studying X-rays from hot gas surrounding our Milky Way galaxy.

HaloSat, a new CubeSat mission to study the halo of hot gas surrounding the Milky
Way, was released from the International Space Station over Australia on July 13.
Credits: NanoRacks/NASA

---

The cosmic microwave background (CMB) is the oldest light in the universe, radiation from when it was 400,000 years old. Calculations based on CMB observations indicate the universe contains: 5 percent normal matter protons, neutrons and other subatomic particles; 25 percent dark matter, a substance that remains unknown; and 70 percent dark energy, a negative pressure accelerating the expansion of the universe.

As the universe expanded and cooled, normal matter coalesced into gas, dust, planets, stars and galaxies. But when astronomers tally the estimated masses of these objects, they account for only about half of what cosmologists say should be present. ...

Researchers think the missing matter may be in hot gas located either in the space between galaxies or in galactic halos, extended components surrounding individual galaxies.

HaloSat will study gas in the Milky Way’s halo that runs about 2 million degrees Celsius (3.6 million degrees Fahrenheit). At such high temperatures, oxygen sheds most of its eight electrons and produces the X-rays HaloSat will measure. ...

[saturno2]

Very interesting

[neufer]

Standing Buddha with a halo, 1st century AD.

---

<<A galactic halo is an extended, roughly spherical component of a galaxy which extends beyond the main, visible component. Several distinct components of galaxies comprise the halo:

• the stellar halo
  the galactic corona (hot gas, i.e. a plasma)
  the dark matter halo

The distinction between the halo and the main body of the galaxy is clearest in spiral galaxies, where the spherical shape of the halo contrasts with the flat disc. In an elliptical galaxy, there is no sharp transition between the other components of the galaxy and the halo. The stellar halo is a nearly spherical population of field stars and globular clusters. It surrounds most disk galaxies as well as some elliptical galaxies of type cD. A low amount (about one percent) of a galaxy's stellar mass resides in the stellar halo, meaning its luminosity is much lower than other components of the galaxy.

The Milky Way's stellar halo contains globular clusters, RR Lyrae stars with low metal content, and subdwarfs. Stars in our stellar halo tend to be old (most are greater than 12 billion years old) and metal-poor, but there are also halo star clusters with observed metal content similar to disk stars. The halo stars of the Milky Way have an observed radial velocity dispersion of about 200 km/s and a low average velocity of rotation of about 50 km/s. Star formation in the stellar halo of the Milky Way ceased long ago.

A galactic corona is a distribution of gas extending far away from the center of the galaxy. It can be detected by the distinct emission spectrum it gives off, showing the presence of HI gas and other features detectable by X-ray spectroscopy.

The dark matter halo is a theorized distribution of dark matter which extends throughout the galaxy extending far beyond its visible components. The mass of the dark matter halo is far greater than the mass of the other components of the galaxy. Its existence is hypothesized in order to account for the gravitational potential that determines the dynamics of bodies within galaxies. The nature of dark matter halos is an important area in current research in cosmology, in particular its relation to galactic formation and evolution.>>