This troupe of four galaxies, known as Hickson Compact Group 87 (HCG 87), is performing an intricate dance orchestrated by the mutual gravitational forces acting between them. The dance is a slow, graceful minuet, occurring over a time span of hundreds of millions of years.
The Wide Field and Planetary Camera 2 on NASA's Hubble Space Telescope (HST) provides a striking improvement in resolution over previous ground-based imaging. In particular, this image reveals complex details in the dust lanes of the group's largest galaxy member (HCG 87a), which is actually disk-shaped, but tilted so that we see it nearly edge-on. Both 87a and its elliptically shaped nearest neighbor (87b) have active galactic nuclei which are believed to harbor black holes that are consuming gas. A third group member, the nearby spiral galaxy 87c, may be undergoing a burst of active star formation. Gas flows within galaxies can be intensified by the gravitational tidal forces between interacting galaxies. So interactions can provide fresh fuel for both active nuclei and starburst phenomena. These three galaxies are so close to each other that gravitational forces disrupt their structure and alter their evolution.
From the analysis of its spectra, the small spiral near the center of the group could either be a fourth member or perhaps an unrelated background object.
The HST image was made by combining images taken in four different color filters in order to create a three-color picture. Regions of active star formation are blue (hot stars) and also pinkish if hot hydrogen gas is present. The complex dark bands across the large edge-on disk galaxy are due to interstellar dust silhouetted against the galaxy's background starlight. A faint tidal bridge of stars can be seen between the edge-on and elliptical galaxies.
HCG 87 was selected for Hubble imaging by members of the public who visited the Hubble Heritage website (http://heritage.stsci.edu) during the month of May and registered their votes. The HST exposures of the winning target were then acquired in July 1999 by the Hubble Heritage Team and guest astronomers Sally Hunsberger (Lowell Observatory, Flagstaff, Arizona) and Jane Charlton (Pennsylvania State University).
Credits
The Hubble Heritage Team (AURA/STScI/NASA)| About The Object | |
|---|---|
| Object Name | Hickson Compact Group 87, HCG 87 |
| Object Description | Cluster of Interacting Galaxies |
| R.A. Position | 20h 48m 10.99s |
| Dec. Position | -11° 50' 24.0" |
| Constellation | Capricornus |
| Distance | 120 Mpc (roughly 400 million light-years) |
| Dimensions | The galaxy group has a diameter of 52 kpc (170,000 light-years). |
| About The Data | |
| Data Description | Principal Astronomers: J. Charlton (PSU), S. Hunsberger (Lowell Obs.), F. Hamilton, H. Bond, C. Christian, J. English, L. Frattare, A. Kinney, Z. Levay, K. Noll (The Hubble Heritage Team (STScI/AURA) |
| Instrument | HST>WFPC2 |
| Exposure Dates | July 19-25, 1999, Exposure Time: 6.6 hours |
| Filters | F450 (B), F555W (V), F675W (R), and F814W (I) |
| 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. |
