This diagram shows how scientists determined the size of the halo of the Andromeda galaxy. Because the gas in the halo is dark, the team measured it by using the light from quasars, the very distant bright cores of active galaxies powered by black holes. They observed the quasars' light as it traveled through the intervening gas. The halo's gas absorbed some of that light and made the quasar appear darker in a very small wavelength range. By measuring the tiny dip in brightness at that specific range, scientists could tell how much gas is between us and each quasar. Some quasars showed no dip in brightness, and this helped define the size of the halo.
Credits
Illustration: NASA, ESA, and A. Feild (STScI);Science: NASA, ESA, N. Lehner and J.C. Howk (University of Notre Dame), and B. Wakker (University of Wisconsin, Madison)
| About The Object | |
|---|---|
| Object Name | M31, Andromeda Galaxy, Messier 31, NGC 224 |
| Object Description | Spiral Galaxy, halo |
| R.A. Position | 00h 42m |
| Dec. Position | +41° 15' |
| Constellation | Andromeda |
| Distance | Redshift: 2.5 million light-years (0.8 megaparsecs) |
| About The Data | |
| Data Description | Ultraviolet observations of multiple quasi-stellar objects (QSOs) seen through the extended circumgalactic medium around M31 were obtained from various HST proposals. Studies of these archival data led to the results found. The science team comprises: N. Lehner and J.C. Howk (University of Notre Dame), and B. Wakker (University of Wisconsin, Madison). |
| Instrument | HST>COS/FUV |
| Filters | Gratings: G130M, G160M |
| About The Object | |
|---|---|
| Object Name | A name or catalog number that astronomers use to identify an astronomical object. |
| Object Description | The type of astronomical object. |
| R.A. Position | Right ascension – analogous to longitude – is one component of an object's position. |
| Dec. Position | Declination – analogous to latitude – is one component of an object's position. |
| Constellation | One of 88 recognized regions of the celestial sphere in which the object appears. |
| Distance | The physical distance from Earth to the astronomical object. Distances within our solar system are usually measured in Astronomical Units (AU). Distances between stars are usually measured in light-years. Interstellar distances can also be measured in parsecs. |
| Dimensions | The physical size of the object or the apparent angle it subtends on the sky. |
| About The Data | |
| Data Description |
|
| Instrument | The science instrument used to produce the data. |
| Exposure Dates | The date(s) that the telescope made its observations and the total exposure time. |
| Filters | The camera filters that were used in the science observations. |
| About The Image | |
| Image Credit | The primary individuals and institutions responsible for the content. |
| Publication Date | The date and time the release content became public. |
| Color Info | A brief description of the methods used to convert telescope data into the color image being presented. |
| Orientation | The rotation of the image on the sky with respect to the north pole of the celestial sphere. |
