Supermassive Black Hole in Milky Way Galaxy

The presence of an enormous black hole at the center of our galaxy has been detected by a researcher funded, in part, by the National Science Foundation (NSF). The evidence is being reported this week at the Central Parsecs Galactic Center Workshop '98 in Tucson, Arizona, by Andrea Ghez, of the University of California-Los Angeles.

"What lies in the center of the Milky Way has been one of this century's 'big' science questions," said Terry Oswalt, NSF program manager for Stellar Astronomy and Astrophysics. "Ghez's work has massive implications on our understanding of how galaxies evolve."

Black holes are formed from the remnants of collapsed stars. A black hole consists of a large mass compacted so densely that not even light can escape its force of gravity. Since Ghez could not directly see a black hole, she inferred its presence by searching for the gravitational influence it imposes on nearby objects she could see, namely stars.

In 1995, using the Keck I Telescope atop Mauna Kea in Hawaii, Ghez began tracking the movement of 200 stars near the galactic center. She found at least 20 stars that exhibited the telling signs of influence by extreme gravitational forces.

These stars are spiraling around the black hole at speeds of up to three million miles per hour-about 10 times the speed at which stars typically move. In order to account for the rapid speeds of these stars, Ghez determined that an object 2.6 million times more massive than our Sun must be concentrated into a single black hole.

Just getting a clear view of the center of our galaxy is an impressive feat in itself. To overcome the distortion created by the Earth's atmosphere, Ghez made her observations using a technique called "infrared speckle interferometry." The procedure, which she helped develop, uses computers to analyze thousands of high-speed, high-resolution snapshots.

The result: an image that has at least 20 times better resolution than those made by traditional earthbound imaging techniques. "It's like putting on glasses," said Ghez.

Using this technique in 1995, Ghez witnessed the disappearance of a star that was, at the time, the closest object to the black hole. Whether the star was sucked into the black hole, or simply went behind it, scientists may never know.

But we have little to fear about a similar fate for Earth, since the center of the Milky Way galaxy is approximately 24,000 light years away. Because of the Earth's position on an outer arm of the spiraling Milky Way, much of our knowledge about galaxies does not come from our own. Ghez's research, however, gives us a definitive view about a part of Galaxy that we have never seen before.

"There is an incredible amount of matter between us and the center of the Milky Way to obscure our view," said Oswalt. "Ghez has pulled the living room shades open a bit and finally given us a good look at what's going on in our own backyard."

Supermassive black hole

Supermassive black hole

Introduction:

A supermassive black hole is the largest type of black hole in a galaxy, on the order of hundreds of thousands to billions of solar masses. Most, if not all galaxies, including the Milky Way, are believed to contain supermassive black holes at their centers.

Formation:

There are many models for the formation of black holes of this size. The most obvious is by slow accretion of matter starting from a black hole of stellar size. Another model[5] of supermassive black hole formation involves a large gas cloud collapsing into a relativistic star of perhaps a hundred thousand solar masses or larger. The star would then become unstable to radial perturbations due to electron-positron pair production in its core, and may collapse directly into a black hole without a supernova explosion, which would eject most of its mass and prevent it from leaving a supermassive black hole as a remnant. Yet another model involves a dense stellar cluster undergoing core-collapse as the negative heat capacity of the system drives the velocity dispersion in the core to relativistic speeds. Finally, primordial black holes may have been produced directly from external pressure in the first instants after the Big Bang.

The difficulty in forming a supermassive black hole resides in the need for enough matter to be in a small enough volume. This matter needs to have very little angular momentum in order for this to happen. Normally the process of accretion involves transporting a large initial endowment of angular momentum outwards, and this appears to be the limiting factor in black hole growth, and explains the formation of accretion disks.

Currently, there appears to be a gap in the observed mass distribution of black holes. There are stellar-mass black holes, generated from collapsing stars, which range up to perhaps 33 solar masses. The minimal supermassive black hole is in the range of a hundred thousand solar masses. Between these regimes there appears to be a dearth of intermediate-mass black holes. Such a gap would suggest qualitatively different formation processes. However, some models suggest that ultraluminous X-ray sources (ULXs) may be black holes from this missing group.

Perseid Meteor Shower

Perseid Meteor Shower:

It's a good night when a beautiful alignment of planets is the second best thing that's going to happen.

Thursday, August 12th, is such a night.

The show begins at sundown when Venus, Saturn, Mars and the crescent Moon pop out of the western twilight in tight conjunction. All four heavenly objects will fit within a circle about 10 degrees in diameter, beaming together through the dusky colors of sunset. No telescope is required to enjoy this naked-eye event: sky map.

A Perseid meteor photographed in Aug. 2009 by Pete Lawrence of Selsey, UK. [more]

The planets will hang together in the western sky until 10 pm or so. When they leave, following the sun below the horizon, you should stay, because that is when the Perseid meteor shower begins. From 10 pm until dawn, meteors will flit across the starry sky in a display that's even more exciting than a planetary get-together.

The Perseid meteor shower is caused by debris from Comet Swift-Tuttle. Every 133 years the huge comet swings through the inner solar system and leaves behind a trail of dust and gravel. When Earth passes through the debris, specks of comet-stuff hit the atmosphere at 140,000 mph and disintegrate in flashes of light. These meteors are called Perseids because they fly out of the constellation Perseus.

Swift-Tuttle's debris zone is so wide, Earth spends weeks inside it. Indeed, we are in the outskirts now, and sky watchers are already reporting a trickle of late-night Perseids. The trickle could turn into a torrent between August 11th and 13th when Earth passes through the heart of the debris trail.

2010 is a good year for Perseids because the Moon won't be up during the midnight-to-dawn hours of greatest activity. Lunar glare can wipe out a good meteor shower, but that won't be the case this time.

As Perseus rises and the night deepens, meteor rates will increase. For sheer numbers, the best time to look is during the darkest hours before dawn on Friday morning, Aug. 13th, when most observers will see dozens of Perseids per hour.

Looking northeast around midnight on August 12th-13th. The red dot is the Perseid radiant. Although Perseid meteors can appear in any part of the sky, all of their tails will point back to the radiant.

For best results, get away from city lights. The darkness of the countryside multiplies the visible meteor rate 3- to 10-fold. A good dark sky will even improve the planetary alignment, allowing faint Mars and Saturn to make their full contribution to the display. Many families plan camping trips to coincide with the Perseids. The Milky Way arching over a mountain campground provides the perfect backdrop for a meteor shower.

Enjoy the show!

New Asteroid threat!

Although scientists have basically cleared us from any danger from asteroid 2002 NT7, which originally had been reported as an impact hazard for the year 2019, a newer space rock has been spotted, which may pose a threat even sooner.

At around 1.2 km in width, 2003 QQ47 is substantially smaller than 2002 NT7 (2km), but has been called "an event meriting careful monitoring" by astronomers. If an impact does occur, it could be on March 21, 2014.

Discovered on August 24, 2003, by the Lincoln Near Earth Asteroid Research Project (an MIT Lincoln Laboratory program funded by the United States Air Force and NASA) in New Mexico, 2003 QQ47 has been classified as a 1 on the Torino scale of impact hazards. Scientists are urging calm, however, saying the odds of a catastrophic collision are only around 1 in 909,000.

The orbit of this asteroid has been calculated on only 51 observations during a seven-day period and require further observations to determine if any danger does exist. It will be monitored closely over the next two months. Astronomers expect the risk of impact to decrease significantly as more data is gathered.

If it does strike Earth, the impact could have the effect of over 20 million Hiroshima style atomic bombs. As Billy Bob Thornton says in Armageddon, “It's what we call a Global Killer....the end of mankind. Half the world will be incinerated by the heat blast.....the rest will freeze to death in a nuclear winter. Basically, the worst part of the Bible!”

Asteroids are rocks and debris which are the leftovers of the construction of our solar system nearly 5 billions years ago. Most are in a belt, which orbits the sun between Mars and Jupiter. However, the gravitational influence of the gas giant planets, like Jupiter, or an impact by a comet can knock these large rocks out of their safe orbit.

Needless to say, we will be monitoring this situation very closely.

Update:

Once again, the planet can breathe a sigh of relief. After making further observations of asteroid 2003 QQ47, astronomers now say there is no threat from this rock. It has been downgraded to a zero (0) on the Torin scale, which says, "The likelihood of a collision is zero, or well below the chance that a random object of the same size will strike the Earth within the next few decades. This designation also applies to any small object that, in the event of a collision, is unlikely to reach the Earth's surface intact."

While this particular asteroid appears to not be a threat to Earth at this time, the Near Earth Object Program and other agencies continue to monitor space for other threats. After all, it is a big universe, and there are a lot of asteroids and comets out there.