A NASA Hubble Space Telescope (HST) view of the magnificent spiral galaxy NGC 4603, the most distant galaxy in which a special class of pulsating stars called Cepheid variables have been found. It is associated with the Centaurus cluster, one of the most massive assemblages of galaxies in the nearby universe. The Local Group of galaxies, of which the Milky Way is a member, is moving in the direction of Centaurus at a speed of more than a million miles an hour under the influence of the gravitational pull of the matter in that direction.
Clusters of young bright blue stars highlight the galaxy's spiral arms. In contrast, red giant stars in the process of dying are also found. Only the very brightest stars in NGC 4603 can be seen individually, even with the unmatched ability of the Hubble Space Telescope to obtain detailed images of distant objects. Much of the diffuse glow comes from fainter stars that cannot be individually distinguished by Hubble. The reddish filaments are regions where clouds of dust obscure blue light from the stars behind them.
This galaxy was observed by a team affiliated with the HST Key Project on the Extragalactic Distance Scale. Because NGC 4603 is much farther away than the other galaxies studied with Hubble by the Key Project team, 108 million light-years, its stars appear very faint from the Earth, and so accurately measuring their brightness, as is required for distinguishing the characteristic variations of Cepheids, is extremely difficult. At this distance some non-variable stars may by chance appear to grow brighter and fainter in the same fashion as Cepheids due to the physical impossibility of perfect measurements of such dim objects. Determining the distance to the galaxy required an unprecedented statistical analysis based on extensive computer simulations.
Researchers found 36-50 Cepheids and used their observed properties to securely determine the distance to NGC 4603. These measurements indicate that when the expansion of the universe and the motion of the Local Group are accounted for, the Centaurus cluster is very nearly at rest compared with the surrounding regions. It is part of the cause of the rapid motions in the nearby universe, rather than being strongly pulled by other concentrations of matter. Observations of distant Cepheids such as those in NGC 4603 also help astronomers to precisely measure the expansion rate of the universe.
Credits
Jeffrey Newman (Univ. of California at Berkeley) and NASA| About The Object | |
|---|---|
| Object Name | NGC 4603 |
| Object Description | Spiral Galaxy |
| R.A. Position | 12h 40m 55.69s |
| Dec. Position | -40° 58' 33.99" |
| Constellation | Centaurus |
| Distance | 108 million light-years (33 million parsecs) |
| About The Data | |
| Instrument | HST>WFPC2 |
| Exposure Dates | May - July, 1996; June - July, 1997 |
| 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. |
