Supermassive Black Holes Spin at the Limits of Relativity

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You know the saying: nothing, not even light can escape a black hole. That makes them invisible. Amazingly, researchers from the University of Maryland have determined how fast a supermassive black hole is spinning. You won’t be surprised to know it’s spinning insanely fast, at the limits predicted by relativity.

The researchers used ESA’s XMM-Newton X-Ray telescope to examine the quantity of iron in an accretion disk around a supermassive black hole at the centre of galaxy MCG-06-30-15. Because the disk is spinning so rapidly, the light from the disk is warped relativistically. According to their calculation, the black hole must be spinning at least 98.7% of the maximum spin rate allowable by Einstein’s Theory of General Relativity.

This result helps astronomers understand how black holes grow over time. If supermassive black holes formed by slowly pulling in surrounding matter, they would be expected to spin faster and faster, until they reach this relativistic limit. If the supermassive black holes were instead formed by colliding smaller black holes, they’d be spinning much more slowly.

Original Source: UM News Release

Dark Matter Annihilation at the Centre of the Milky Way

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Most of the Universe is a complete and total mystery. And one of these mysteries is dark matter. It’s out there, and astronomers are slowly teasing out its characteristics, but it’s not giving up its secrets easily. The problem is, dark matter only interacts with regular matter through gravity (and maybe through the weak nuclear force). It doesn’t shine, it doesn’t give off heat or radio waves, and it passes through regular matter like it isn’t there. But when dark matter is destroyed, it might give astronomers the clues they’re looking for.

Researchers have theorized that one productive way to search for dark matter might not be to search for it directly, but to look for the resulting particles and energy which are emitted when it’s destroyed. In the environment around the centre of our galaxy, dark matter might be dense enough that particles regularly collide, releasing a cascade of energy and additional particles; which could be detected.

And this theory could help account for a strange result gathered by the Wilkinson Microwave Anisotropy Probe (WMAP), a NASA spacecraft which is mapping the temperature of the Cosmic Microwave Background Radiation (CMBR). This background radiation was supposed to be roughly even across the entire sky. But for some reason, the satellite turned up an excess of microwave emission around the centre of our galaxy.

Perhaps this microwave radiation is the glow of all that dark matter getting annihilated.

This conclusion was reached by a team of US astronomers: Dan Hooper, Douglas P. Finkbeiner and Gregory Dobler. Their work is published in a new research paper called Evidence Of Dark Matter Annihilations In The WMAP Haze.

The excess microwave radiation around our galactic centre is known as the WMAP Haze, and was originally thought to be the emissions from hot gas. Astronomers set about trying to confirm this theory, but observations in other wavelengths failed to turn up any evidence.

According to the researchers, the microwave haze could be explained by annihilating particles of dark matter, like the interaction between matter and antimatter. As dark matter particles collide they could give off any number of detectable particles and radiation, including gamma-rays, electrons, positrons, protons, antiprotons and neutrinos.

The size, shape and distribution of the haze matches the central region of our galaxy which should also have a high concentration of dark matter. And if the dark matter particles are within a certain range of mass – 100 to 1000s of times the mass of a proton – they could release a torrent of electrons and positrons that nicely match the microwave haze.

In fact, their calculations precisely match one of the most attractive dark matter particle candidates: the hypothetical neutralino which is predicted in supersymmetry models. When annihilated, these would produce heavy quarks, gauge bosons or the Higgs boson, and would have the right mass and particle size to produce the microwave haze observed by WMAP.

One of the predictions made in this paper is for the upcoming Gamma Ray large Area Space Telescope (GLAST), due to launch in December, 2007. If they’re correct, GLAST will be able to detect a glow of gamma rays coming from the Galactic Centre, matching the microwave haze, and even put an upper limit of the mass of dark matter particles. The upcoming ESA Planck mission will give an even more precise look at the microwave haze, providing better data.

It might still be mysterious, but dark matter is revealing its secrets slowly but surely.

Original Source: Arxiv (PDF)

Dwarf Galaxy is Falling Into our Local Group for the First Time

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Life isn’t easy for a dwarf galaxy in our local group. They’re passed from galaxy to galaxy, harassed by gravity, and eventually torn up and consumed when they get to close to a large galaxy like our own Milky Way. But astronomers have turned up an example of a new class of dwarf galaxy, ones which formed very far away, and just arrived at the party.

The new dwarf galaxy is called Andromeda XII, and it was discovered during a wide-field survey taken with the Canada-France Hawaii Telescope’s “MegaCam” instrument. It’s one of the faintest dwarf galaxies ever discovered near the Andromeda galaxy (M31), and it probably has the lowest mass ever measured.

Instead of being one of these dwarf galaxies that’s suffered billions of years of galactic harassment, Andromeda XII is on a fast moving, highly eccentric orbit, which means it’s falling into the Local Group of galaxies for the first time. And since it lived its life apart from these galactic interactions, it’s a pristine object to study. Its rate of star formation, the size and shape of its dark matter halo and evolution weren’t influenced by other galaxies.

Andromeda XII is moving so quickly that it probably won’t even be captured by the Local Group, passing right through to destinations unknown.

Original Source: W.M. Keck Observatory News Release

Massive Binary System Discovered

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Many of the stars in the Universe are located in binary or multiple star system, where several stars orbit a common centre of gravity. But astronomers have discovered an extreme binary system, where two of the largest possible stars orbit one another.

The discovery was made using NASA’s Far Ultraviolet Spectroscopic Explorer (FUSE) satellite, as well as ground-based observatories. FUSE turned up a system called LS54-425 in the Large Magellanic Cloud, a satellite galaxy of the Milky Way. This system contains two stars: one with 37 times the mass of the Sun, and the other is 62 solar masses.

Although they’re extremely massive, these two type-O stars only orbit one another at 1/6th the distance between the Earth and the Sun, completing an orbit within 2.25 days. Both stars are generating massive solar winds, which collide, giving off X-rays and ultraviolet radiation. And this is how FUSE was able to spot them.

The more massive star is shedding material about 400 times as fast as our Sun, and the smaller star gives off about 40 times as much material. As they age and grow, the two stars will transfer a tremendous amount of material to each other, and eventually they will merge, creating a single star of 100 times the mass of the Sun.

And then, within just a few million years, this super star will detonate as a very energetic supernova.

Original Source: NASA News Release

Snow Melt is on the Rise in Greenland

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The island of Greenland experienced more days of melting during 2006 on average than in the last 18 years, according to new NASA-funded research.

The data were gathered by the Special Sensor Microwave Imaging radiometer (SSM/I) flying aboard the Defense Meteorological Satellite Program spacecraft. It can peer through the clouds, and measure the rates of melting every day. During 2006, researchers estimated that portions of Greenland melted for an additional 10 days beyond averages.

Melting water on Greenland will impact global water levels. But the water can also slip down through cracks in glaciers, and lubricate the ice sheet. This can speed up the movement of glaciers, which eject ice into the ocean, and further accelerate sea level rise.

Original Source: NASA News Release

Astrosphere for May 29, 2007

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Time for another turn around the astrosphere.

I know I went on and on yesterday about how I’m not able to attend the International Space Development Conference. Well, I’m going to continue living vicariously through the attendees.

And the busiest of the bunch is Space Prizes. Here are a torrent of posts, including: X-Prize Cup details, Armadillo Aerospace, and an Automotive X-Prize (100 mpg cars anyone?).

One of my favourite sites is The Space Review. Each week they’ve got a handful of really interesting articles and opinion pieces about space exploration. Here’s an example from this week’s issue, how the CIA was monitoring the Soviet manned lunar program by Dwayne Day.

And finally, here’s a nice picture of the M57, the Ring Nebula, one of my favourite telescope targets. Thanks to Vern’s Weblog.

“The Universe” on the History Channel

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I’m pleased to announce a new sponsor for Universe Today and Astronomy Cast: “The Universe” brought to you by the History Channel. This is a 13-week documentary series about, what else, the Universe.

The first episode starts on Tuesday, May 29 at 9:00pm (8:00pm Central), and it’s called – “Secrets of the Sun”. There’s another showing Wednesday morning at 1:00am.

Here’s the blurb about it:

It is a fireball in the sky, a bubbling, boiling, kinetic sphere of white hot plasma, exploding and erupting. Its size is almost unimaginable–one million Earths would fit within its boundaries. In this violence is born almost all the energy that makes existence on Earth possible, yet, its full mysteries are only now beginning to be understood. From Sun spots to solar eclipses, solar flares to solar storms, the birth of the sun to its potential death, discover the science and history behind this celestial object that makes life on Earth exist.

So make sure you tune in over the Summer. If you’d like more information about the show, check out their special website at: http://history.com/universe

Astrosphere for May 28, 2007

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It may be Memorial Day in the US, but it’s just a regular working day here in Canada. So, here’s today’s fine list of finds.

First, I’d like to point you towards the 5th Carnival of Space. It’s out of my hands this time, but I’ll be submitting an article. You should too.

If there was one conference I wish I could attend, it’s the International Space Development Conference going on in Houston. Unfortunately, I don’t pay me enough to attend conferences, but lots of people are there. I’ll just live vicariously through them.

Here’s a report from Spaceflight Sandbox.

More from ISDC, this time Space Liberates Us! is talking about Rick Tumlinson’s plans to create the sport of spacediving. That’s skydiving… but from space.

And Jeff Faust from Personal Spaceflight has news on Jim Benson’s new Dream Chaser spacecraft.

But that’s not the only conference I’m missing. This week is the American Astronomical Society’s meeting in Hawaii. Pamela Gay is there, and blogging all about it. Get ready for a hailing storm of space news.

Centauri Dreams is dreaming big.

Medium-Sized Black Hole Lurks in a Star Cluster

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Supermassive black holes lurk at the heart of galaxies, containing the mass of millions of stars. Stellar mass black holes can contain the mass of a few suns. But astronomers have been perplexed why they haven’t been able to turn up intermediate mass black holes, containing merely hundreds or thousands of times the mass of our Sun.

Well, now they have. Astronomers using the NSF’s Very Large Array (VLA) radio telescope have turned up a globular cluster in the Andromdeda Galaxy (M31) that seems to contain a black hole with the mass of 20,000 times the mass of the Sun; one of these long-sought intermediate black holes.

Researchers originally detected X-rays emitted from this globular cluster, and then did follow up observations in the radio spectrum to confirm that a high mass, compact object is inside the cluster. Although the best explanation is a black hole, it could also be a cluster of compact objects, like neutron stars and black holes. The quantity of radio emissions coming from the object fits the curve perfectly between stellar and supermassive black holes.

Original source: NRAO News Release

Grand Spiral Galaxy M81 by Hubble

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Astronomers released this beautiful photograph of the grand spiral design galaxy, M81, captured by the Hubble Space Telescope. Although it looks like a single image, it was actually constructed by stitching together many images on computer, using three different wavelengths of light.

M81 is located about 11.6 million light-years in the constellation of Ursa Major. We’re fortunate that it’s turned at an oblique angle towards the Earth, so we can see a full view of the spiral structure. Hubble’s view of M81 is so crisp and clear that individual stars can be resolved, as well as open clusters and globular star clusters.

The older, redder stars are contained around the galaxy’s central bulge, and it has regions of star formation along its spiral arms. Astronomers suspect that its recent nearby encounter with another galaxy (M82) unleashed the period of star formation about 300 million years ago.

The image was released as part of the Americal Astronomical Society Meeting in Honolulu, which is currently going on in Hawaii.

Original Source: Hubble News Release