This composite image shows a region in the halo in the neighboring Andromeda galaxy that astronomers used to precisely measure the galaxy's sideways motion on the sky. This has allowed them to predict a direct collision between Andromeda and the Milky Way about 4 billion years from now.
The inset image on the left is from a 2002 Hubble Space Telescope deep exposure that captured the light from 300,000 stars in Andromeda's halo, a vast spherical cloud of stars surrounding the galaxy's bright disk. Embedded in the image are numerous background galaxies that are much father away than Andromeda.
Astronomers compared this region to pictures of the same area taken seven years later. They measured the tiny amount of sideways drift in the halo stars relative to the stationary background galaxy field. The same measurements were done for two other fields in the galaxy as well. This is similar to measuring the drift of a boat relative to a background shoreline.
Credits
NASA, ESA, R. van der Marel and T. Brown (STScI), and the Digitized Sky Survey| About The Object | |
|---|---|
| Object Name | M31, NGC 224, Andromeda Galaxy |
| Object Description | Starfield in M31 |
| R.A. Position | 00h 42m 44s |
| Dec. Position | +41° 16' 9" |
| Constellation | Andromeda |
| Distance | About 2.5 million light-years (770 kiloparsecs) |
| About The Data | |
| Data Description | The Hubble data were taken from the HST proposals and , PI: T. Brown (STScI); and , PI: R. van der Marel (STScI). The science team comprises: R. van der Marel, S.T. Sohn, J. Anderson, and T. Brown (STScI), M. Fardal (University of Massachusetts, Amherst), G. Besla (Columbia University), R. Beaton (University of Virginia), P. Guhathakurta (UCO/Lick Observatory/UCSC), and T.J. Cox (Carnegie Observatories). |
| Instrument | HST>ACS/WFC and HST>WFC3/UVIS |
| Exposure Dates | December 2002 and January 2005; January 2010 and August 2010 |
| Filters | ACS/WFC: F606W (V) and F814W (I) WFC3/UVIS: F606W (V) |
| About The Image | |
| Color Info | This image is a composite of separate exposures acquired by the ACS instrument on HST. Several filters were used to sample broad wavelength ranges. The color results from assigning different hues (colors) to each monochromatic (grayscale) image associated with an individual filter. In this case, the assigned colors are: Blue: F606W (V) Red: F814W (I) |
| Compass Image |  |
| 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. |
