Astronomers now believe there's a supermassive black hole at the centre of almost every galaxy in the Universe. These black holes can have millions, or even hundreds of millions of times the mass of the Sun. Unlike stellar mass black holes, the supermassive versions might have formed differently, going from a cloud of gas directly to a black hole - skipping the star stage entirely.
Since their discovery, astronomers still don't really know how supermassive black holes got going. But there they are, inside most galaxies. In fact, quasar observations show that supermassive black holes were present in the early Universe. Quasars are some of the brightest objects in the Universe, blazing from the radiation emitted by supermassive black holes actively consuming material.
One possibility is that these monsters had humble beginnings, starting out as a massive star, going supernova, and then becoming a black hole. It's a process astronomers understand fairly well. The problem with this theory is that these early supermassive black holes must have been growing constantly right from the beginning, at the maximum rate predicted by physics. And as we see today, galaxies go through active and quiescent stages depending on when their black hole is consuming material.
But a second possibility is that these black holes formed directly, pulling together so much material that they bypassed the stellar stage entirely.
Dr. Mitchell C. Begelman, a professor in the Department of Astrophysical and Planetary Sciences at the University of Colorado, Boulder recently published a paper entitled Did supermassive black holes form by direct collapse? This paper sketches out this alternate theory of black hole formation in the early Universe.
After the Big Bang, the Universe cooled enough for the first stars to form out of the original hydrogen and helium. This was pure material, unpolluted by previous generations of stars. Astronomers have calculated that these first stars, called Population III, would have a maximum rate that they could gather material together to form a star.
But what if there was much more gas around? Way beyond the limits that could form a star.
With a regular star, material comes in relatively slowly, creating a central mass. With enough mass, the star ignites, and this creates and outward pressure that stops further material from compacting too tightly.
But Dr. Begelman has calculated that if the infall rate exceeds just a few tenths of a solar mass per year, the stellar core would be so tightly bound that the energy release of nuclear fusion wouldn't be enough to stop the core from continuing to contract. You would never have a star, you would just go from a cloud of hydrogen to a tightly bound central mass. And then a black hole.
The question is, would it be possible to have material come together so quickly? It can, if something's pushing it… like dark matter. According to Dr. Begelman, there could be several situations where an external force, like the gravity from a large halo of dark matter which could work to force gas into a central area. In fact, material has been calculated falling into a black hole this quickly, because that's the rate it takes to power quasars. But the question is, will this work if the black hole isn't there, or really small.
Once there are a few solar masses of accumulated gas, the core begins to shrink under the pull of its increasing mass. The object goes through a brief period of nuclear fusion when it reaches 100 solar masses, but it passes through this phase so rapidly that it doesn't get a chance to expand again.
Eventually the object reaches several thousand solar masses, and its temperature has climbed to several hundred million degrees. At this point, gravity finally takes over, collapsing the core, and turning the object into a 10-20 solar mass black hole which then starts consuming all the mass around it.
From this point on, the black hole is able to draw in further material efficiently, growing at the maximum levels predicted by physics, eventually gathering up millions of times the mass of the Sun. If too much material falls in, the baby supermassive black hole might act like a mini-quasar - Dr. Begelman has dubbed this a "quasistar" - blazing with radiation as infalling material backs up in the black hole's surroundings.
And there's the good news: these quasistars might be detectable by powerful telescopes. However, they would have very short lifetimes, only lasting 100,000 years. They might be marginally detectable by the upcoming James Webb Space Telescope.
- from the topic: Never a Star: Did Supermassive Black Holes Form Directly?
Heaviest Stellar Mass Black Hole Discovered
October 17, 2007 by fcain
Black Holes come in two varieties: supermassive and stellar. The supermassive variety can have millions of times the mass of a star, while the stellar varieties are usually just a few times the mass of a single sun. Using the Chandra X-Ray Observatory, astronomers have turned up the most massive stellar mass black hole ever seen, weighing in at 15.7 times the mass of the Sun, lurking in a nearby galaxy.
M33 is a relatively nearby galaxy, located only 3 million light years from Earth. This newly discovered black hole has been designated as M33 X-7.
Astronomers using NASA's Chandra X-Ray Observatory and the Gemini telescope on Mauna Kea were able to precisely determine the black hole's mass because it's actually in a binary system. Its binary partner is unusual too; a star with 70 times the mass of the Sun.
M33 X-7 orbits its companion star every 3.5 days, briefly passing behind it. This blocks the torrent of X-rays streaming from the environment around the black hole, so that astronomers were able to calculate its orbit. Once they could calculate the orbits of the two binary objects, it's relatively straightforward to calculate their respective masses.
The fate of the companion star will eventually match its partner. "This is a huge star that is partnered with a huge black hole," said coauthor Jeffrey McClintock of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. "Eventually, the companion will also go supernova and then we'll have a pair of black holes."
Although the black hole has less mass today, it must have started out with more. With more mass in the original star, it would have consumed its fuel more quickly, and detonated as a supernova earlier.
Here's a puzzle, though. Before the black hole formed, the two stars wouldn't have been able to orbit so closely. In fact, they would have been orbiting inside each other. This means that they were once further apart, and the process of sharing their outer atmospheres brought their orbits closer together.
Original Source: Chandra News Release
Re: Highlighting new posts
October 11, 2007 by fcain
Yeah, that's what happens. I just wrote that post, and now there's a new one to read. And when I post this one, I assume there'll be another.
Re: Highlighting new posts
October 11, 2007 by fcain
Maybe it took you to your latest post, not realizing that you're wrote it, so there's no point displaying it to you again.
Re: Highlighting new posts
October 11, 2007 by fcain
I'm starting to get the hang of that. I like that visual difference. There's also the X new replies up at the top right-hand corner of the page; although, it could become overwhelming when we're adding 500 new posts a day.
Re: Depth of categories
October 11, 2007 by fcain
Or even some way to logically organize them. For example, something like:
BLOGS
- Bad Astronomy
- Universe Today
- Astronomy
- Astrophotos
- Space Exploration
- Etc.
Depth of categories
October 10, 2007 by fcain
From what I could tell setting things up, you can create a single level of categories, and that's it. Are there plans to deepen it? For example, I'd want to break up "Discussion Forum" into similar categories that we currently have on BAUT. And instead of having sections for UT and BA, I might just have a category called "Blogs", with those two nestled underneath. That would give room for growth.
Re: Initial impressions
October 10, 2007 by fcain
The hot topics are great for new users coming to the forum for the first time to get a sense of the community. Repeat users will already have a sense of the ongoing conversations, and will much prefer to know what's new and changed, to update their mental picture of the state of the forum.
It might sound insane, but you might want to present a different front end depending on whether it's a new user or a registered user, or even on a cookie basis.
Re: Highlighting new posts
October 10, 2007 by fcain
I was just going to mention something like that. It's hard to know what's new and changed since the last time I came here. Perhaps I'm missing the feature?
Presentation of Subsections
October 10, 2007 by fcain
I was thinking that you might want the main page of each subsection to mimic the homepage. For example, when I go to the main page, there's that big picture highlighted from one of the stories. But when I click on the Universe Today subsection, it would be cool to have something similar, instead of just a listing of all the stories.
http:/
Re: Initial impressions
October 10, 2007 by fcain
The volume question is a concern for me as well. We create about 40 new threads a day, and there are about 500-700 new posts a day. I think the biggest challenge is information architecture. How do you present that volume of new information without hiding it away? How do you present the hottest threads, but still give newer threads a chance. There must be a better way to do it than vBulletin.
High Energy Gamma Rays Go Slower Than the Speed of Light?
October 5, 2007 by fcain
The speed of light is the speed of light, and that's that. Right? Well, maybe not. Try and figure this out. Astronomers studying radiation coming from a distant galaxy found that the high energy gamma rays arrived a few minutes after the lower-energy photons, even though they were emitted at the same time. If true, this result would overturn Einstein's theory of relativity, which says that all photons should move at the speed of light. Uh oh Einstein.
The discovery was made using the new MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov) telescope, located on a mountain top on the Canary island of La Palma. Since gamma rays are blocked by the Earth's atmosphere, astronomers have figured out a clever trick to see them from the ground. When the gamma rays strike the atmosphere, they release a cascade of particles and radiation. The Cherenkov technique detects this cascade, and then works backwards to calculate the direction and energy level of the gamma rays. With a 17-metre detector, MAGIC is the largest telescope of its type.
The international team of researchers pointed the telescope at Markarian 501, a galaxy 500 million light-years away that contains a blazar - a supermassive black hole that periodically releases bursts of gamma rays. More material is falling into the black hole than it can consume, and so it gets squeezed into jets that fire off from the poles of the black hole at close to the speed of light. What astronomers call a "blazar" is when the jets of a supermassive black hole are pointed directly at the Earth.
Researchers sorted high- and low-energy gamma ray photons coming from the blazar with each flareup. Since all the radiation was emitted at the same time, and the speed of light is the speed of light, you would expect the high-energy photons to arrive at the same time. But nope, the high-energy photons showed up around 4 minutes later.
So what's happening? Nobody knows, and this could turn into an entirely new field of physics. The researchers are proposing that maybe the radiation is interacting with "quantum foam". This is a theoretical property of space itself, and predicted by quantum gravity theory - a competitor to string theory.
Original Source: UC Davis News Release
NASA is Building the Third Tallest Roller Coaster in the World, as an Escape System
October 5, 2007 by fcain
Let's hope that nothing ever goes wrong while astronauts are preparing to launch on their Ares 1 rocket - the new vehicle that will replace the space shuttle. But if there is a problem, and the astronauts need to escape right now, they'll have a fun ride down - on the 3rd tallest roller coaster in the world. It's called the Orion Emergency Egress System, but really, it's a roller coaster, designed to get the astronauts away from the vehicle and into a protective bunker in moments.
Take a good look at the image that goes along with this story. See the bright yellow rails over on the right hand side of the image, dropping straight down from the gray platform. That's the escape system. You'll note it goes straight down.
The purpose of the Orion Emergency Egress System is to get astronauts and support personnel away from the Ares 1 vehicle, and into a safety bunker within 4 minutes. The solution that NASA has come up with should be perfect, carrying astronauts and workers down away from the rocket, right to the bunker's door.
For previous launch vehicles, NASA had cables near the door to the launch vehicle. If there was a problem, people could enter a basket that slides down a cable to an area near the bunker. The problem was that it was very difficult to get incapacitated people into the basket and down to the safety of the bunker. With the new egress system, healthy workers can just put the wounded in seats and let them ride down to safety.
NASA called in the world's roller coaster designers to help them create the system. In fact, from a height of 116 metres (380 feet), the Orion Emergency Egress System would be the third tallest roller coaster in the world, after the Kingda Ka at Six Flags Great Adventure in Jackson, New Jersey, and the Top Thrill Dragster at Cedar Point in Sandusky, Ohio.
Original Source: NASA News Release
Re: Never a Star: Did Supermassive Black Holes Form Directly?
September 10, 2007 by fcain
I agree with the author's article.
Never a Star: Did Supermassive Black Holes Form Directly?
September 10, 2007 by fcain
Astronomers now believe there's a supermassive black hole at the centre of almost every galaxy in the Universe. These black holes can have millions, or even hundreds of millions of times the mass of the Sun. Unlike stellar mass black holes, the supermassive versions might have formed differently, going from a cloud of gas directly to a black hole - skipping the star stage entirely.Since their discovery, astronomers still don't really know how supermassive black holes got going. But there they are, inside most galaxies. In fact, quasar observations show that supermassive black holes were present in the early Universe. Quasars are some of the brightest objects in the Universe, blazing from the radiation emitted by supermassive black holes actively consuming material.
One possibility is that these monsters had humble beginnings, starting out as a massive star, going supernova, and then becoming a black hole. It's a process astronomers understand fairly well. The problem with this theory is that these early supermassive black holes must have been growing constantly right from the beginning, at the maximum rate predicted by physics. And as we see today, galaxies go through active and quiescent stages depending on when their black hole is consuming material.
But a second possibility is that these black holes formed directly, pulling together so much material that they bypassed the stellar stage entirely.
Dr. Mitchell C. Begelman, a professor in the Department of Astrophysical and Planetary Sciences at the University of Colorado, Boulder recently published a paper entitled Did supermassive black holes form by direct collapse? This paper sketches out this alternate theory of black hole formation in the early Universe.
After the Big Bang, the Universe cooled enough for the first stars to form out of the original hydrogen and helium. This was pure material, unpolluted by previous generations of stars. Astronomers have calculated that these first stars, called Population III, would have a maximum rate that they could gather material together to form a star.
But what if there was much more gas around? Way beyond the limits that could form a star.
With a regular star, material comes in relatively slowly, creating a central mass. With enough mass, the star ignites, and this creates and outward pressure that stops further material from compacting too tightly.
But Dr. Begelman has calculated that if the infall rate exceeds just a few tenths of a solar mass per year, the stellar core would be so tightly bound that the energy release of nuclear fusion wouldn't be enough to stop the core from continuing to contract. You would never have a star, you would just go from a cloud of hydrogen to a tightly bound central mass. And then a black hole.
The question is, would it be possible to have material come together so quickly? It can, if something's pushing it… like dark matter. According to Dr. Begelman, there could be several situations where an external force, like the gravity from a large halo of dark matter which could work to force gas into a central area. In fact, material has been calculated falling into a black hole this quickly, because that's the rate it takes to power quasars. But the question is, will this work if the black hole isn't there, or really small.
Once there are a few solar masses of accumulated gas, the core begins to shrink under the pull of its increasing mass. The object goes through a brief period of nuclear fusion when it reaches 100 solar masses, but it passes through this phase so rapidly that it doesn't get a chance to expand again.
Eventually the object reaches several thousand solar masses, and its temperature has climbed to several hundred million degrees. At this point, gravity finally takes over, collapsing the core, and turning the object into a 10-20 solar mass black hole which then starts consuming all the mass around it.
From this point on, the black hole is able to draw in further material efficiently, growing at the maximum levels predicted by physics, eventually gathering up millions of times the mass of the Sun. If too much material falls in, the baby supermassive black hole might act like a mini-quasar - Dr. Begelman has dubbed this a "quasistar" - blazing with radiation as infalling material backs up in the black hole's surroundings.
And there's the good news: these quasistars might be detectable by powerful telescopes. However, they would have very short lifetimes, only lasting 100,000 years. They might be marginally detectable by the upcoming James Webb Space Telescope.
