Posted on 06/04/2009 3:07:32 PM PDT by Fred Nerks
SYDNEY: The universe's first stars blew small galaxies apart when they exploded, effectively quashing all nearby star formation, say Japanese astrophysicists.
The theory, based on analytical calculations of the energy and disruptive effects of early supernovae, adds another piece to the puzzle of what the first stars were like and how they influenced galaxy formation.
The first stars formed around 200 million years after the Big Bang in clumps of dark matter called dark matter haloes the basic building blocks of galaxies.
Running out of gas
These stars were massive, probably 10 to 100 times bigger than the Sun. Like most massive stars, they would have burnt through their fuel within a few tens of millions of years and then exploded as either a type II supernova or a pair instability supernova.
The study, published in the current issue of the Astrophysical Journal, looks at what happened to the dark haloes near these massive explosions. Previously, experts were divided as to whether the first supernovae kick started star formation in the haloes or suppressed it.
Astrophysicists Masaru Sakuma from the University of Tsukuba, in Tsukuba, and Hajime Susa from Konan University in Kobe, Japan, say their model shows the shockwave from these supernovae would have expanded the gas shell within the stars' own galaxies, creating a gaseous 'wind' that stripped the gas out of nearby dark haloes.
First clues
This 'wind' would have swept the gas from dark haloes within a radius of up to 5,000 light-years around the supernova, depending on the force of the initial explosion and the mass of the dark haloes, the researchers say.
"[If] a neighbouring halo is located very close to the centre of the supernova explosion, the gas in the halo would be evacuated by the shock momentum... supernova feedback has basically negative effects on the star formation in surrounding halos," the researchers write.
Commenting on the research, Australian theoretical astrophysicist Stuart Wyithe, from the University of Melbourne, said the research answered a "little bit" of the big question of how the death of the first stars affected the early universe.
"Early galaxies are analogous to buckets of gas, with the gas confined by gravity rather than by walls. The supernova explosion blows the gas out of the first bucket. This moving gas then acts like a wind which in turn blows the gas out of small nearby galaxies," Wyithe said.
"[The research] doesn't address other issues about how much gas there is in the first place and what happens when there are many haloes [surrounding the supernovae]," he said. But added that the study is "solid piece of work."
"Analytic calculations like these can sometimes give quite good information, and I think in this case it does," said Wyithe. "It's not understood fully what role the first stars played in the reionisation of the early universe. This is a first step on the way to understanding that."
A pair instability supernova occurs when the furnace of reactions in the heart of a star are no longer powerful enough to act against its massive gravity. Then the star collapses spectacularly, as seen here in an image of supernova remnant E0102-72.
the original suicide bomber?
in clumps of dark matter called dark matter haloes the basic building blocks of galaxies.
The existence of dark mater is still pretty controversial I believe.
You are probably right, but I can never anticipate the ever changing past.
ELECTRIC UNIVERSE!
http://www.newscientist.com/article/dn14696-is-dark-matter-a-wimp-or-a-champ.html
The mysterious dark matter that makes up most of the material in the universe may actually have an electric charge, a new study suggests. If so, it might help explain why astronomers see so few dwarf galaxies in orbit around larger ones.
Dark matter is detected by its tug on light and visible matter, so astrophysicists have largely assumed that it interacts mostly through the force of gravity and not electromagnetism, for example. Indeed, the leading dark matter candidates, known as weakly interacting massive particles, or WIMPs, are electrically neutral.
But theorists Leonid Chuzhoy and Rocky Kolb of the University of Chicago say it may be time to consider the possibility that dark matter is actually composed of charged massive particles, or CHAMPs. That would mean magnetic fields could push on or deflect dark matter adding another way for it to interact with the known universe.
The idea for CHAMPs is not new it was actually discarded more than a decade ago, after underground particle detectors failed to pick up any sign of such candidates.
Now, a new analysis suggests the particles may exist just not in our galactic neighbourhood. That’s because the shape of the Milky Way’s magnetic field could prevent CHAMPs from entering the galaxy’s disc of stars, where the Earth resides.
‘Prematurely rejected’
Any CHAMPs in the disc would have been cast out long ago, slingshotted outwards by the magnetic fields of rapidly expanding supernovae remnants, the team says.
“We have to keep our minds open about what dark matter could be,” Kolb told New Scientist. “I think it’s a brilliant idea that could have been prematurely rejected.”
Avi Loeb of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, agrees that it is worth keeping an open mind. “The nature of dark matter is not known, so it’s always healthy and important to explore unconventional possibilities,” he told New Scientist.
If dark matter is electrically charged, it would be more likely to collide with normal matter. That’s because it could couple with ordinary matter through its magnetic fields. Normal matter might also bounce off its electrostatic fields like a billiard ball.
Massive particles
The researchers are currently studying what properties CHAMPs would need to explain dark matter observations.
For example, CHAMPs must bump into normal matter fairly rarely in order to create cosmic displays like the Bullet Cluster and MACS J0025. In these collisions of galaxy clusters, ordinary matter gets jumbled up in the crash but dark matter continues on unimpeded.
Finding CHAMPs may prove tricky. The proposed particles would weigh at least 100,000 times the mass of the proton, too heavy to be created by the world’s most powerful particle accelerator, the Large Hadron Collider, which is set to start up on Wednesday.
Their weight might also make them difficult to observe in space. Charged particles such as electrons and protons emit radiation when they are accelerated by magnetic fields, but CHAMPs would be too massive to produce much light, says the team.
Still, neutral versions of the particles could be found on Earth, says Chuzhoy. If CHAMPs are negatively charged, they might have bound to iron and other elements to create supermassive varieties that could be detected by their weight. These elements might also absorb and emit telltale X-rays that could be observed by telescopes.
Missing dwarfs
Charged dark matter could help explain some cosmic conundrums.
Because CHAMPs would collide more often with normal matter, they could blast gas from growing dwarf galaxies. This could inhibit star formation and explain why astronomers see so few dwarf galaxies in orbit around the Milky Way and nearby giants.
Since CHAMPs can be accelerated by the magnetic fields in stellar explosions, the particles might also explain why there seems to be less dark matter at the centres of dwarf galaxies than simulations predict.
But Loeb notes that the Milky Way’s magnetic field might not prevent CHAMPs from reaching the planet.
That’s because charged particles from beyond the galaxy do manage to reach Earth. Mysterious ultra-high energy cosmic rays, for example, appear to enter the Milky Way along ‘open’ magnetic field lines.
Chuzhoy suggests that some of these cosmic rays could actually be CHAMPs.
Smoothed out
If dark matter is charged, it could have had a drastic effect on the universe soon after the big bang.
When the universe was very dense, particles of light, or photons, smoothed out subtle ripples in ordinary matter. But dark matter is supposed to have remained clumpy after the big bang, creating small pockets of mass that drew in surrounding material to form larger structures such as galaxies.
If photons can collide with CHAMPs, that might make dark matter smooth as well. “You wouldn’t be able to make galaxies at later times,” Loeb told New Scientist. “[The researchers] have to do more work to make it a viable scenario.”
I think of dark matter as a kind of cipher. A place holder that fills out the theory until they figure out what’s really is going on.
Thanks Fred Nerks for posting
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Looking down at the top of Carrot Top's head?
IIRC, it’s a remnant of a supernova in Tycho...
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“All we know is that it acts like matter in that it causes gravity. . “
I disagree that even that much is “known”. I find ALL dark matter speculations very unconvincing, and the current “evidence” seems, to this physicist, as interesting but also greatly overreaching.
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