December 5, 2012
Astronomers Identify New Type Of Rare Galaxy
[ Watch the Video: The Green Bean Galaxy J2240 ]
Lee Rannals for redOrbit.com - Your Universe Online
Astronomers using the European Space Observatory's Very Large Telescope (VLT) have identified a new galaxy class.
The "green bean galaxies" have an unusual appearance, glowing in intense light emitted from the surroundings of monster black holes.
The galaxies are amongst the rarest objects in the universe, and in the case of green bean galaxies, the entire galaxy glows, not just its center.
New observations have revealed the largest and brightest glowing regions ever found, thought to be powered by central black holes that were formerly active but are not switching off.
Astronomer Mischa Schirmer of the Gemini Observatory looked at many images of the distance Universe in search of galaxy clusters. He was stunned when he came across one object in an image from the Canada-France-Hawaii Telescope.
The object looked like a galaxy, but was bright green, and unlike any galaxy he had ever seen before. He quickly applied to use the VLT to find what was creating the unusual green glow.
“ESO granted me special observing time at very short notice and just a few days after I submitted my proposal, this bizarre object was observed using the VLT,” Schirmer said. “Ten minutes after the data were taken in Chile, I had them on my computer in Germany. I soon refocused my research activities entirely as it became apparent that I had come across something really new.”
The new object, J224024.1-092748 or J2240, lies in the constellation of Aquarius, and its light has taken about 3.7 billion years to reach Earth.
After the discovery, the astronomers searched through a list of nearly a billion other galaxies and found 16 more with similar properties to J2240. These galaxies are so rare that there is only one in a cube of about 1.3 billion light-years across.
Green bean galaxies were given their nickname because of their color and because they are superficially similar to green pea galaxies.
Many galaxies contain material around their supermassive black holes at the center, giving off intense radiation and ionizing the surrounding gas so it glows strongly. The glowing regions in typical active galaxies are small. However, in the case of J2240 and other green beans spotted, the glowing regions are huge, spanning the entire object.
J2240 displays one of the biggest and brightest such regions ever found. Ionized oxygen glows green, explaining the strange color that originally caught Schirmer's eye.
“These glowing regions are fantastic probes to try to understand the physics of galaxies – it´s like sticking a medical thermometer into a galaxy far, far away,” Schirmer said. “Usually, these regions are neither very large nor very bright, and can only be seen well in nearby galaxies. However, in these newly discovered galaxies they are so huge and bright that they can be observed in great detail, despite their large distances.”
Further analyses made by the team soon revealed that J2240 had a much less active black hole at its center than expected. The team believes that the glowing regions must be an echo from when the black hole was more active in the past
“Discovering something genuinely new is an astronomer's dream come true, a once-in-a-lifetime event,” concludes Schirmer. “It's very inspiring!”
The astronomers reported their findings in The Astrophysical Journal.