Press Release
Discovery of Huge Gas Cloud Expanding around Galaxy
April 15, 2002
 Low Res. (110KB) Mid Res. (431KB) High Res. (1.5MB) |
Object Name: Active Galaxy NGC 4388 Telescope: Subaru Telescope / Prime Focus Instrument: Suprime-Cam Filter: [OIII] narrow-band (0.50micron), V (0.55 micron), Halpha (0.66micron) Color: Blue ([OIII] narrow-band), Green (V) , Red (Halpha) Date: UT 2001 March 24, April 24, 26 Exposure: 60 min ([OIII] narrow-band) , 15 min (V), 160 min (Halpha) Field of View: approx. 11.6 arcmins x 5 arcmins Orientation: North up, east left Position: RA(J2000.0)=12h30.8m, Dec(J2000.0)=+12d23m (Virgo) |
Observations with Suprime-Cam
on Subaru Telescope have detected for the first time long
filaments of ionized hydrogen gas extending 110,000 light
years above the disk of a galaxy. In the new image, the
gas shows up in red and purple and appears to burst out
of the center of the galaxy, reaching as far as the upper-left
corner of the image. This galaxy, called NGC 4388, belongs
to the Virgo Cluster, a large group of galaxies some 60
million light years from our own Milky Way galaxy. These
observations provide new clues to how galaxies evolve inside
the dense environment of a cluster of galaxies.
NGC 4388 belongs to a class of galaxies known as "active
galaxies"; these objects are believed to harbor at
their centers super-massive black holes that are a million
times heavier than our Sun and are swallowing gas from their
host galaxies in a process called accretion. Accretion produces
vast amounts of energy which can outshine the light from
all the stars in the galaxy and excite gas so that it loses
an electron and becomes ionized. When hydrogen recombines
with the electron, it emits light at a specific wavelength,
allowing astronomers to see it.
It was previously known that NGC 4388 had ionized gas extending
10,000 light years from the center of the galaxy, but these
new results are puzzling as the energy produced by the black
hole can only ionize gas for a distance of 50,000 light
years. An additional source of ionization may be required
to explain the more extended ionized hydrogen gas. As a
comparison, the ionized gas in NGC 4388 extends ten times
further than the
ionized gas in M 82 that is seen in the image taken by FOCAS
on Subaru Telescope and released to the public in March
2000.
As for the original source of the hydrogen gas, there are
several processes that can occur in a galaxy cluster that
may be responsible. One possibility is ram pressure stripping,
in which the gas that was originally inside NGC 4388 gets
stripped away as it passes through gas that is associated
with the cluster as a whole. Another possibility is that
NGC 4388 may have swallowed a nearby dwarf galaxy.
In the near future, astronomers hope to take spectra of
the light emitted by the ionized gas to determine its velocity
and details of its ionization state. Understanding the origin
of the hydrogen gas in NGC 4388 and how it becomes ionized
will contribute to the larger understanding of how galaxies
evolve in the dense environment of a galaxy cluster. Clusters
contain anywhere between a few dozen galaxies to several
thousand galaxies, and are part of the fundamental pattern
of how matter is distributed throughout the Universe. The
Virgo Cluster is the cluster closest to the Milky Way.
Michitoshi Yoshida who analyzed this data says: "I
never expected to see such extended ionized gas around NGC
4388. This can really help us understand the origin of gas
surrounding galaxies, and its physical state."
These results were published in the Astrophysical Journal
on March 1st.
Notes: The large streaks of light from the bright stars
in the image are artifacts called "blooming" and
are not real. When too much light hits a digital camera
in one spot, the light spills over onto other areas. If
you look at the image carefully, you can see several small
streaks. These are solar system objects that were moving
during the observation.
(*) NGC: Abbreviation of New General Catalog of Nebula and Cluster of Stars published in 1888
