Using the new, high-frequency capabilities of the National Science Foundation’s Robert C. Byrd Green Bank Telescope (GBT), astronomers have captured never-before-seen details of the nearby starburst galaxy M82. These new data highlight streamers of material fleeing the disk of the galaxy as well as concentrations of dense molecular gas surrounding pockets of intense star formation.
“With this new vision, we were able to look at M82 to explore how the distribution of molecular gas in the galaxy corresponded to areas of intense star formation,” said Amanda Kepley, a post-doctoral fellow at the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia, and lead author on a paper accepted for publication in the Astrophysical Journal Letters. “Having this new capability may help us understand why stars form where they do.”
Astronomers recognize that dense molecular gas goes hand-in-hand with areas of star formation, but the connection is poorly understood and this relationship may be different in different types of galaxies. By creating wide-angle maps of the gas in galaxies, astronomers hope to better understand this complex interplay.
To date, however, these kinds of observations have not been easy since molecules that are used to map the distribution of dense gas, like HCN (hydrogen cyanide) and HCO+ (formylium), shine feebly in millimeter light. With its new W-Band receiver, the GBT was able to make highly sensitive, wide-angle images of these gases in and around M82.
“The GBT data clearly show billowing concentrations of dense molecular gas huddled around areas that are undergoing bursts of intense star formation,” said Kepley. “They also reveal giant outflows of ionized gas fleeing the disk of the galaxy. These outflows are driven by star formation deep within the galaxy.”
This capability will enable astronomers to quickly survey entire galaxies and different parts within galaxies. Such surveys would complement higher resolution observations with new Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile.
In April 2010, radio astronomers working at the Jodrell Bank Observatory of the University of Manchester reported an unknown object in M82. The object has started sending out radio waves, and the emission does not look like anything seen anywhere in the universe before.
The plausibility of a supernova explanation was further undermined when very accurate positional monitoring by the UK network of radio telescopes, MERLIN, tentatively detected a change in position for the object over the first 50 days. This was equivalent to an apparent superluminal motion of over 4 times the speed of light. Such large apparent velocities are not seen in supernova remnants and are usually only found with relativistic jets ejected from accretion disks around massive black hole systems.The nucleus of M82, like most major galaxies, is expected to contain a super-massive black hole.
The new detection lies at a position close to, but several arcseconds from the dynamical centre of M82 -- far enough away that it would seem unlikely that this object is associated with the central collapsed core of this galaxy.
The new source could be the first radio detection of an extragalactic 'micro-quasar'. Examples of such systems within the Milky Way are found as X-ray binaries with relativistic jets ejected from an accretion disk around a collapsed star fuelled with material dragged from a close binary companion.
However, this object would be brighter than any Galactic example yet detected, has lasted months longer than any known X-ray binary, and lies at a position in M82 where no variable X-ray source has been yet been detected.
If this object is an extragalactic micro-quasar, it would be the first that has been detected at radio wavelengths. The very high luminosity suggests that it is likely to be associated with a massive black hole system of some type; however this and its longevity imply that this type of object is extremely unusual and has not yet been seen within the Mily Way.
There have been several theories about the nature of this unknown object, but currently no theory entirely fits the observed data. The problem with the "micro quasar" theory is microquasars produce large quantities of X-rays, whereas no X-rays have been seen from the mystery object.The object is located at several arcseconds from the center of M82.
Infrared telescopes have found a very strong wind emanating from M82 — a 'superwind' that is composed of dusty gas and extends over many hundreds of thousands of light years (middle and bottom of image). This high-powered windstorm ejects material from the galaxy at a speed of about a half a million miles per hour, sweeping it up from the central regions and depositing it far and wide over the galaxy and beyond. The contents of this material are seeds for solar systems like our own, and perhaps for life itself. The dusty superwind glows brightly in the infrared, because billions of bright, newly-formed stars heat it up.
"The wind is found to originate from multiple ejection sites spread over hundreds of light years rather than emanating from any single cluster of new stars. We can now distinguish 'pillars' of fast gas , and even a structure resembling the surface of a 'bubble' about 450 light years wide."
An exciting question that remains to be answered is whether or not M 82 hosts an actively growing supermassive black hole. Team members Drs. Mark Birkinshaw and Diana Worrall of the University of Bristol note, "Detailed analysis of the new infrared data combined with X-rays does not find any such object." However, all large galaxies could well contain these monsters, which are known to grow and evolve in conjunction with stars. The team concludes that M 82 may be no exception, and the search for its big black hole must continue.
The radio-optical image below shows five new clouds of hydrogen gas discovered using the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT). The spiral galaxy M81 and its satellite, M82, are seen in visible light (white); intergalactic hydrogen gas revealed by the GBT is shown in red; and additional hydrogen gas earlier detected by the Very Large Array is shown in green.
The M81 Group of galaxies, 11.8 million light-years from Earth, are interacting gravitationally with each other, as shown clearly by the gas streaming among them. The newly-discovered gas clouds, each containing from 14 to 57 million times the mass of our Sun, are similar to gas clouds also found near our own Milky Way Galaxy. Astronomers analyzing these M81 Group clouds conclude that they are likely remnants of earlier interactions among the galaxies and that this indicates that their analogs near the Milky Way had a similar origin.
The Daily Galaxy via NRAO
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