Monday, May 28, 2007
A Hyperactive Brown Dwarf
The following Space.com excerpt wants you to consider a brown dwarf that is spewing jets of material into space, much the same way as a hot young star, or even a black hole would do. Check it out:
A "failed star" with only 24 times the mass of Jupiter is the smallest known object to spout jets of matter from its poles, a phenomenon typically associated with much larger black holes and young stars.
The new finding, detailed in the current issue of Astrophysical Journal, confirms that a wide range of celestial objects is capable of generating such outflows.
"There are black holes that are 3 million solar masses spewing jets, and there's this thing, which is 2 percent of a solar mass, doing the same thing," said study team member Ray Jayawardhana of the University of Toronto. The discovery also raises the possibility that large gas giant planets like Jupiter or Saturn might also have been gushers some time early in their history.
The new jet-spewing object is a previously identified brown dwarf-celestial objects with masses between 13 and 75 times that of the Jupiter, too massive to be a planet but too small to sustain the internal nuclear fires needed to become stars. For this reason, brown dwarfs are sometimes called failed stars.
Called 2M1207a, the spurting brown dwarf is ringed by gas and dust, similar to the protoplanetary disks from which planets form around young stars. Indeed, 2M1207a is known to harbor a 5-Jupiter-mass planetary companion. Called 2M1207b, the gas giant was one of the first planets outside of our solar system to have its picture taken directly.
2M1207a's streaming jets were discovered using the European Southern Observatory's Very Large Telescope (VLT). The jets extend about 620 million miles (1 billion km) into space and are speeding away from the brown dwarf at a few kilometers per second.
"Preliminary results suggest that a brown-dwarf jet is just scaled down from what we see in a low mass star," said study leader Emma Whelan of the Dublin Institute for Advanced Physics in Ireland. In 2005, Whelan's team discovered the first jet-spewing brown dwarf, but that one was about 60 Jupiter masses.
Scientists are still not sure of the role jets play in star formation. One idea is that by ejecting large amounts of material into space, the jets help determine the final size and mass of the star.
Another hypothesis is that jets actually play a major role in initiating star formation in the first place. Stars are thought to form from enormous, spinning clouds of gas and dust that somehow collapse and contract into blazing balls of fire. To do this, the clouds must get rid of a lot of spin energy, or "angular momentum."
"One of the best ways to get rid of that is to put it into a jet," Jayawardhana told SPACE.com. "So these jets might actually be spinning and carrying out the angular momentum of the formed object."
The new gushing nature of 2M1207a could help shed light on how jets are formed and sustained.
Do we live in amazing times or what? It was just a few years ago that the notion of a brown dwarf was still a theory. The discoveries of these objects was one thing, to find them behaving this way is quite another.
The dumping of mass to slow, or eliminate angular momentum makes sense, as this is regularly observed behavior in young stars. Perhaps the key is that the cloud of matter out of which stars are born are too small in the case of a brown dwarf, and therefore, even when exhibiting the youthful matter ejection most stars display, the amount of mass ejected may be too much to ignite the process to make the brown dwarf shine as a true star.
It will be interesting to see what develops with this story, as I'm sure other brown dwarfs will be watched carefully to see if they behave in a manner similar to that of 2M1207a.