 |
|
Stellar still births
August 25, 2008The systematics of celestial bodies apparently needs to be revised. Researchers at the Argelander Institute of Astronomy of the University of Bonn have discovered that brown dwarfs need to be treated as a separate class in addition to stars and planets. To date they had been merely regarded as stars which were below normal size. However, they may well be stellar 'miscarriages'. The astronomers are publishing their results in the journal Monthly Notices of the Royal Astronomical Society. A preview can be seen at http://arxiv.org/abs/0808.2644.
Brown dwarfs (or BDs) are what scientists call objects which populate the galaxies apart from the stars. Unlike the latter, they cannot develop high-yield hydrogen fusion as in the interior of our sun due to their low mass (less than about 8% of the sun's mass). But in addition to this brown dwarfs and stars also seem to be different in their 'mating behaviour'.
Stars often occur in pairs, which dance around each other. The intimacy which this dance involves, however, varies a great deal: sometimes the gap is smaller than one radius of the Earth's orbit (also known as Astronomical Unit or AU). However, the two partners can also keep apart by as much as many thousands of AUs. 'Things are different with brown dwarfs,' astrophysicist Ingo Thies of the Bonn Argelander Institute of Astronomy explains. 'The orbital radiuses of BD pairs are cut off above about 15 AUs; BD pairs with greater distances are the exception.'
What is more, there are hardly any mixed pairs consisting of suns and brown dwarfs - far fewer than expected. This phenomenon is also known as brown dwarf desert. 'According to the classical model there ought not to be these differences,' Professor Pavel Kroupa of the Argelander Institute explains. 'According to this both brown dwarfs and stars ought to emerge from interstellar clouds of gas which become concentrated because of the attraction of their mass. But if this was the case, these celestial bodies should behave in similar ways.'
Despite this contradiction the astronomic community has previously stuck to the theory of a joint origin. However, Ingo Thies and Pavel Kroupa have now shown empirically for the first time that brown dwarfs must be seen as a class of objects which is separate from the stars. 'For this we analysed the masses of newly born stars,' Ingo Thies explains. 'This revealed a jump in the distribution of mass which makes the division in the stellar population apparent.'
Death of an embryonic star
But how are brown dwarfs born? As long ago as 2001 the Danish researcher Bo Reipurth, Britain's Cathie Clarke and the Spanish astronomer Eduardo Delgado-Donate had the idea that brown dwarfs could be interpreted as stellar 'miscarriages': a system consisting of three embryonic stars disintegrates due to the mutual attraction of masses, and the lightest object is catapulted out of the system. The physical mechanism itself has long been known: even the US light space probes Pioneer and Voyager were hurled off onto their voyage of no return by the planet's gravity.
Another possibility would be that brown dwarfs form in the outermost regions of emergent stars and become separated from them. This can, for example, occur as the result of a close encounter with a third star. Since almost all stars are born in star clusters, such encounters are not unusual. It is also possible that both scenarios of cosmic miscarriages take place.
Both theories predict that brown dwarfs can only emerge at the birth of stars - similar to the situation with planets, incidentally. Thus there are presumably three quite different celestial bodies: planets, brown dwarfs and stars.
University of Bonn
What is more, there are hardly any mixed pairs consisting of suns and brown dwarfs - far fewer than expected. This phenomenon is also known as brown dwarf desert. 'According to the classical model there ought not to be these differences,' Professor Pavel Kroupa of the Argelander Institute explains. 'According to this both brown dwarfs and stars ought to emerge from interstellar clouds of gas which become concentrated because of the attraction of their mass. But if this was the case, these celestial bodies should behave in similar ways.'
Despite this contradiction the astronomic community has previously stuck to the theory of a joint origin. However, Ingo Thies and Pavel Kroupa have now shown empirically for the first time that brown dwarfs must be seen as a class of objects which is separate from the stars. 'For this we analysed the masses of newly born stars,' Ingo Thies explains. 'This revealed a jump in the distribution of mass which makes the division in the stellar population apparent.'
Death of an embryonic star
But how are brown dwarfs born? As long ago as 2001 the Danish researcher Bo Reipurth, Britain's Cathie Clarke and the Spanish astronomer Eduardo Delgado-Donate had the idea that brown dwarfs could be interpreted as stellar 'miscarriages': a system consisting of three embryonic stars disintegrates due to the mutual attraction of masses, and the lightest object is catapulted out of the system. The physical mechanism itself has long been known: even the US light space probes Pioneer and Voyager were hurled off onto their voyage of no return by the planet's gravity.
Another possibility would be that brown dwarfs form in the outermost regions of emergent stars and become separated from them. This can, for example, occur as the result of a close encounter with a third star. Since almost all stars are born in star clusters, such encounters are not unusual. It is also possible that both scenarios of cosmic miscarriages take place.
Both theories predict that brown dwarfs can only emerge at the birth of stars - similar to the situation with planets, incidentally. Thus there are presumably three quite different celestial bodies: planets, brown dwarfs and stars.
University of Bonn
University Of Bonn Current Events and University Of Bonn News RSSSubstance tackles skin cancer from 2 sides
By playing it safe and using a two-pronged attack, a novel designer molecule fights malignant melanoma. It was created and tested by an international team of researchers led by the University of Bonn.
Cosmic Lens Reveals Distant Galactic Violence
By cleverly unraveling the workings of a natural cosmic lens, astronomers have gained a rare glimpse of the violent assembly of a young galaxy in the early Universe. Their new picture suggests that the galaxy has collided with another, feeding a supermassive black hole and triggering a tremendous burst of star formation.
Genes may make some people more prone to anxiety
Inborn differences may help explain why trauma gives some people bad memories and others the nightmare of post-traumatic stress. Scientists in Germany and the United States have reported evidence linking genes to anxious behavior. The findings appear in the August issue of Behavioral Neuroscience, published by the American Psychological Association.
Birdsong not just for the birds
Computer scientists from the University of Bonn, in conjunction with the birdsong archives of Berlin's Humboldt University, have developed a kind of 'Big Brother' for birds. This has nothing to do with entertainment, but a lot to do with the protection of nature.
Minimally invasive treatment improves male fertility
A minimally invasive treatment for a common cause of male infertility can significantly improve a couple's chances for pregnancy, according to a new study published in the August issue of Radiology.
Kidney transplants less successful at night
Kidney transplants should be carried out during the day if possible. At least this is the conclusion suggested by a survey just published by urologists and internists at the University of Bonn.
Bonn scientists discover new hemoglobin type
Scientists at the University of Bonn have discovered a new rare type of haemo-globin. Haemoglobin transports oxygen in the red blood corpuscles.
Getting to the roots of hair loss
A healthy individual loses around a hundred hairs a day. Nothing to worry about as long as they are constantly replaced and the losses occur evenly around the whole scalp.
Bonn scientists simulate dinosaur digestion in the lab
Scientists from the University of Bonn are researching which plants giant dinosaurs could have lived off more than 100 million years ago.
Significantly higher success rates with artificial insemination
In future a new method could help some couples who are childless against their will. The microscopic procedure significantly improves the success rate of 'ICSI' (intracytoplasmic sperm injection).
More University Of Bonn Current Events and University Of Bonn News Articles
| © 2008 BrightSurf.com |