For scientist, black holes worth being sucked into
Print Edition
THE recent blockbuster film “Interstellar” is credited with providing a scientifically accurate depiction of a black hole to popular audiences. Yet, for scientists like American astrophysicist John F. Hawley, there are light-years between black holes as they are thought to exist in actual spacetime and as they appear on screen.
According to Hawley, the filmmakers behind “Interstellar” modified “something about what a black hole would really look like because they were afraid that people watching the movie wouldn’t understand what’s going on.”
A professor at University of Virginia (which has had astronomy as an area of specialization since its founding in 1819), Hawley in 2013 won the Shaw Prize for Astronomy, one of the most prestigious honors in the field.
Shanghai Daily caught up with the astronomer as he attended the Black Hole Accretion and AGN Feedback Conference in Shanghai early in the month to learn more about black holes, why scientists love studying them, why we should care about them, and whether Earth is in danger of getting sucked into one some day.
Q: Do black holes exist only in theory or have they been observed? How would we detect them if they are completely black?
A: The black hole itself is completely dark. But outside of the black hole, you have gas that orbits it. Because the gravity is so intense, the orbiting speed is close to the speed of light. And if the gas collides with itself, there is a tremendous amount of high energy, which heats up the gas to very high temperature. Then the gas emits light, before it gets drawn into the black hole.
The heated gas emits light, and the bright heated gas surrounding the black hole is what we call the accretion disk, and it is through the accretion disk that we can detect black holes.
Q: How many have we detected?
A: We can only find the ones that are active — meaning they are drawing matter into them. We have detected about 100 black holes in our galaxy — the Milky Way. They are spread all over the galaxy. There is also one super massive black hole in the center of Milky Way, like in many galaxies. Luckily, it is relatively quiet, not violent.
Q: Will Earth ever get sucked into the super massive black hole or any of the other smaller black holes spread over the Milky Way?
A: No, we are fine.
Q: Are there different types of black holes?
A: There are two categories. The star-sized ones are formed from big stars: 100 times as massive as the sun. When these massive stars come to the end of their lives, the center of the star collapses and leaves behind a black hole.
The super massive black holes at the center of galaxies must have been formed differently. They can be millions — or even billions — of times as massive as the sun. For example, our central massive black hole is four million times as massive as the sun.
Such super massive black holes must have been formed when the galaxy was created, although we don’t fully understand the process yet ... they must have been present since the earliest moments of the universe as we can see.
When you have a great big black hole in the center of a galaxy, the black hole draws gas in. The gas is heated and a lot of hot gas can be blown back out ... into an active galaxy. That is called AGN feedback, and that is a big part of this conference.
We want to learn about how the black hole in the center of the galaxy — basically a power source — affects the rest of the galaxy. We are trying to figure out the relation between what happens down here near black holes and what happens in the galaxy.
Q: You were awarded the prestigious Shaw Prize for Astronomy in 2013, mainly for your research on magneto-rotational instability, what is that and why is it important?
A: My research in on behavior of the gas around the black hole. The issue is, if you have a black hole, and you have the gas orbiting around, the question is, why does the gas just keep orbiting?
It was a mystery, because we knew the gas doesn’t just stay there — but we found no reason why it would become turbulent. Only when it becomes turbulent will it get heated and emit light.
So me and my colleague Steven Balbus discovered that if you have a magnetic field, than you get this magneto-rotational instability, which means that the presence of even a very weak magnetic field changes the property of the gas, making it turbulent.
- About Us
- |
- Terms of Use
- |
-
RSS - |
- Privacy Policy
- |
- Contact Us
- |
- Shanghai Call Center: 962288
- |
- Tip-off hotline: 52920043
- 沪ICP证：沪ICP备05050403号-1
- |
- 互联网新闻信息服务许可证：31120180004
- |
- 网络视听许可证：0909346
- |
- 广播电视节目制作许可证：沪字第354号
- |
- 增值电信业务经营许可证：沪B2-20120012
Copyright © 1999- Shanghai Daily. All rights reserved.Preferably viewed with Internet Explorer 8 or newer browsers.
