Ask an Expert: Why Black Holes Suck. Or Do They?





Janet Anderson, 256-544-0034

Marshall Space Flight Center, Huntsville, Ala.

Janet.L.Anderson@nasa.gov

There are many cultural myths concerning black holes -- several of the myths are perpetuated by television and movies. Black holes have been portrayed as time-traveling tunnels to another dimension, or as cosmic vacuum cleaners sucking up everything in sight. Black holes are really just the evolutionary end points of massive stars. Somehow, this simple explanation makes them no easier to understand.On Thursday, July 15, NASA scientist Jerry Fishman from NASA's Marshall Space Flight Center answered your questions about black holes.Joining the chat is easy. Simply visit this page on Thursday, July 15 from 3-4 p.m. EDT. The chat window will open at the bottom of this page starting at 2:30 p.m. EDT. You can log in and be ready to ask questions at 3:00.See you in chat!Gerald (Jerry) Fishman is a research astrophysicist with NASA's Marshall Space Flight Center and the Chief Scientist for Gamma-ray Astronomy there.He was the Principal Investigator of the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory. This observatory was the second of NASA's Four Great Observatories in Space (after Hubble). It was launched by the Space Shuttle Atlantis in April 1991 and operated until May 2000. The BATSE experiment produced new scientific results on some of the most energetic and violent objects in the Universe, in particular, gamma-ray bursts, the most explosive and most distant objects known. He has lectured extensively on these findings at major universities and planetariums in the US and at numerous scientific conferences abroad. This experiment also serendipitously discovered terrestrial gamma-ray flashes above thunderstorms.Dr. Fishman has over two hundred publications in his research areas. He received the NASA Outstanding Scientific Achievement Award in 1982, 1991 and 1993. He was awarded the Bruno Rossi Prize of the High Energy Astrophysics Division of the American Astronomical Society in 1994, that Division's highest award. In 1996 he became a Fellow of the American Physical Society.Jerry: Hi everyone! Thanks for the early questions. We're working on setting up the chat and will start posting those answered in about 15 minutes. Great to see you, and welcome to the chat!Akarsh_Valsan: Hi, good afternoon Jerry. How are black holes formed?Jerry: Most scientists think that black holes are formed when the centers of very massive stars collapse and can no longer support the overlaying material. These are called solar-mass black holes -- black holes with at least 10x the mass of the sun. Much more massive black holes are called supermassive black holes. These are thought to start by "swallowing" other stars at the center of a galaxy. They start as a small black hole and gradually grow to an enormous size, sometimes as large as a hundred million to a billion times the mass of our sun. Some scientists believe that there are a class of "primordial" or small black holes that formed at the same time the universe formed. These haven't been directly observed, so their reality can't be confirmed. Some of the very small primordial black holes are thought to slowly evaporate over long periods of time, whereas more massive black holes can live for many billions of years.Matt: I understand that their existence is purely theoretical, but can you explain micro black holes. Specifically the theory of their creation, lifespan, death, and the effects that they cause on space around them.Jerry: Some scientists believe that there are a class of "primordial" or micro black holes that formed at the same time the Universe formed. These haven't been directly observed, so their reality can't be confirmed. Some of the very small primordial black holes are thought to slowly evaporate over long periods of time, whereas more massive black holes can live for many billions of years.Akarsh_Valsan: What are the two different types of Black Holes?Jerry: You're probably referring to the "solar mass black holes" and the "supermassive black holes." There may be a third class, simply called "intermediate mass black holes," but this third class is controversial as far as being detected. The other two types have almost certainly been observed.Sammy: What is our nearest black hole?Jerry: Our nearest black hole is probably an object called Cygnus X-1. It's about 30,000 light years away from us and is one of the brightest objects in the X-ray sky.CraigNASA: Can you see a black hole with a normal telescope?Jerry: The black hole itself can't be seen but if it has a nearby star circling it, some material from that star is stripped off and just before it gets sucked into the black hole, it gives off enormous radiation. That's how we observe it. We don't observe the black hole directly, but we observe the effects of the black hole in the binary star system.rahulr96: How would one safely enter a black hole? Or could they?Jerry: I wouldn't want to be that person -- entering a black hole would certainly be fatal because of its enormous gravity!wescott60: Was Albert Einstein first to study black holes?Jerry: There are several scientists before Einstein that realized that enormous gravity could exist. Einstein's equations gave us a method of describing what space and time would be like near a black hole. The term "black hole" itself wasn't coined until the 1960s by a scientist from Princeton, John Archibald Wheeler.Akarsh_Valsan: What are the properties of Black Holes?Jerry: At a large distance from black holes, there really are no effects except for its gravity. This is interesting because, for example, if the sun were a black hole instead of a normal star, we would hardly see its effects because we'd only feel the same amount of gravity and nothing else from the black hole.tonster: How are we able to detect gravitational waves that are created from two black hole collisions. Wouldn't the waves be pulled into the black hole like light?Jerry: When two black hole collide (they actually don't collide, but circle each other until they coalesce) enormous "gravity waves" are thought to be emitted. One ground-based system specifically developed to detect these gravity wave is called LIGO. It's a long, laser-based interferometer system. Details of this system can be found by Googling "LIGO." NASA is planning a much larger space-based version of LIGO called LISA. You may also want to Google "LISA NASA."misty: What is the general temperature of a black hole?Jerry: The black hole itself has very little temperature, but when matter is about to enter the black hole, just before it disappears, it's heated to millions of degrees and emits X-rays. This has been observed in at least a dozen different objects in our own galaxy.sciencejunkie57: Thanks for sharing all this information with us.Jerry: You're very welcome, thanks for being part of the chat!kosig: Do blackholes grow continuously?Jerry: Yes, if there's nearby material they'll gather this material and they'll grow in mass -- but only slightly in size.doga_lover54: Do black holes expand and grow?Jerry: We've found at least a dozen solar mass black holes in our own galaxy. There are probably millions of supermassive black holes at the centers of other galaxies but so far we've only seen a few of the nearest of these.Akarsh_Valsan: Can black holes really suck things up?Jerry: At a distance, black holes really don't have more gravity than normal objects, so at a distance they really won't suck things in any more than a normal object of the same mass.Lori_Anne: Hi, I am wondering how the Doppler effect looks in gamma rays?Jerry: Good question. The enormous gravity of a black hole would Doppler-shift any radiation that comes from or near the edge of a black hole, including gamma rays.sciencejunkie57: Is there any evidence that black holes emit any major amounts of Hawking Radiation?Jerry: No -- Hawking Radiation is still controversial and hasn't been directly observed.Akarsh_Valsan: Do black holes move?Jerry: Black holes move just like any other object would move.JJ_Jordan10: Do you have any idea about what happens inside a black hole?Jerry: It's impossible to see inside of a black hole.PaperChase: Besides LISA, is NASA preparing an other studies of black holes?Jerry: None that I know of.Dell_Conagher: How useful is the analogy that a black hole has the same characteristics as an elementary particle, having spin, magnetic charge and mass?Jerry: It's a good analogy, except that I've never heard of a magnetic field being associated with a black hole.Akarsh_Valsan: How can I see a Black Hole?Jerry: You can't see a black hole directly, but if a black hole is in a binary star system, it can be seen with binoculars, an optical telescope, or an x-ray telescope above the Earth's atmosphere.longsheryl: How big are these black holes?Jerry: The black holes themselves have no size. They're called singularities. It seems strange that they have mass but no size.PaperChase; Can you give us some interesting Web sites to learn more about black holes?Jerry: Look on the right side of this page -- some good links there.Dell_Conagher: What are your thoughts on the theory that the trip past the event horizon could be survived under certain circumstances with a spinning black hole?Jerry: The equations say that as long as you stay outside of the black hole "Schwartzchild Radius," you can survive a trip near it.Fox: Hi Gerald, my question is: What exactly happens when two black holes come within contact of eachother? do they merge? or does something entirely different happen?Jerry: Yes, they merge, and an enormous amount of energy is released.Dell_Conagher: What are your thoughts on white holes?Jerry: "White holes" are theoretically possible, but have never been observed. Many scientists don't think they exist.Lucas_Campos: Does every black hole spin?Jerry: Yes, it's believed that most black holes have spin associated with them because the stars that they formed from were rotating before they became black holes.raglev08: Can't you also detect a black hole by the light being distorted around a blank area in space?Jerry: Yes, black holes distort the space around them so that light passing from objects behind them will seem distorted.linmojay: Is it true that one theoretically could stand at the event horizon point of a blackhole and not be sucked in?Jerry: Yes, that's true.Nazban: How long can a black hole live for?Jerry: Black holes live for billions of years, even longer than the Universe will probably be around.raglev08: Why does time seem to go slower as one gets closer to a black hole? Does it have anything to do with the Event Horizon?Jerry: Yes, it's a natural result of Einstein's equations of general relativity.Dell_Conagher: Do you think that information that passes past an event horizon is lost permamently, or is re-emitted somehow as Hawking Radiation?Jerry: Most scientists think the information is lost permanently. A few scientists think that it's somewhere emitted from a "white hole." I believe that Hawking Radiation refers to other radiation being emitted, mainly from small black holes.Akarsh_Valsan: Do black holes ever get full?Jerry: No, black holes continue to grow as they absorb matter.James: Are black holes involved in hyper novas?Jerry: Many astrophysicists think that hypernovas are the birth place of stellar mass black holes and when they form, they emit gamma ray bursts.Lori_Anne: How do black holes disappear?Jerry: It's thought that once a black hole is formed, it only extremely slowly evaporates and for all intents and purposes, it will live just about forever.CraigNASA: Are there any fatal objects that make it dangerous, or is it just the fact that the gravity would crush you?Jerry: It's just the enormous gravity when you get next to a black hole that would crush you.RyanB: Is it true that no one has detected gravity waves yet?Jerry: Correct, they haven't yet been convincingly detected.Akarsh_Valsan: Can you name some naked eye stars that will turn into black holes eventually?Jerry: There is a star I know of in the constellation Carina that some astronomers think is massive enough to collapse and form a black hole within the next few thousand years or so.RyanB: What are mini black holes and how do they form?Jerry: Some scientists believe that there are a class of "primordial" or small black holes that formed at the same time the universe formed. These haven't been directly observed, so their reality can't be confirmed. Some of the very small primordial black holes are thought to slowly evaporate over long periods of time, whereas more massive black holes can live for many billions of years.Nazban: Are there any NASA projects to study black holes?Jerry: The x-ray and gamma-ray observatories that NASA operates study the surroundings of black holes. LISA and LIGO will attempt to directly observe black hole mergers.James: What is the largest black hole detected so far?Jerry: There are many "active galactic nuclei" that are thought to consist of black holes with extremely large masses. It's hard to tell which one is the largest. Perhaps the closest two are called Centaurus A and M-87.Drew: Do thermo-nuclear runaways and black holes have anything to do with each other?Jerry: No, no relation.Adam: Is it possible that our universe was created from a blackhole from another dimension?Jerry: Most astrophysicists think our Universe was created at the time of the Big Bang, not from a black hole.Nazban: What is a quasar?Jerry: It's simply thought to be a supermassive black hole that's putting out an enormous amount of energy.Fox: Do black holes ever die out?Jerry: They evaporate, but VERY slowly.Scarker: Is it possible for an object to orbit a black hole within its event horizon without being sucked into the center?Jerry: Yes, but its orbit will likely become smaller and eventually it will be sucked into the black hole.Nazban: How is a quasar powered by a black hole when light can't escape it?Jerry: The light doesn't escape from the black hole itself, but instead from matter just before it disappears into the black hole.Akarsh_Valsan: How can a force of gravity escape a black hole?Jerry: Gravity isn't a form of matter, so it can "escape" from a black hole...and it does this at the speed of light.raglev08: I heard the center of our galaxy is actually a black hole, is this true?Jerry: Yes, infrared observations have shown that stars near the center of our galaxy are moving so fast around an object called SGR-A*, that this object can only be explained by being a black hole. It's extremely close to the center of our galaxy.michael: Are there created some new elements in the black holes?Jerry: No, no new elements.Dell_Conagher: Do you believe that singularities are real, or are they just artifacts of incompatible theories of gravity and quantum mechanics?Jerry: Singularities are a result of the equations of general relativity. We're very confident that general relativity works, so we think that singularities are real.Akarsh_Valsan: Can one black hole be formed inside other?Jerry: Probably not. :)JJ_Jordan10: How do black holes bend space-time?Jerry: Again, this comes naturally from the equations of Einstein's theory of general relativity. It was first seen in 1919 during a solar eclipse when light from a distant star was bent as it passed close to the surface of the sun. If space-time weren't true, this wouldn't have happened. It was BIG news in 1919, and it made Einstein famous and a world-wide celebrity.intali: How is it that black holes decrease in mass over time?Jerry: The mass decreases via complicated process called black hole evaporation, or "Hawking Radiation," named for Stephen Hawking.kosig: What happens to any mass that a black hole may gather?Jerry: It causes the black hole to grow in mass and slightly in size.Jackie: Can black holes in the centers of galaxies devour them?Jerry: They won't devour the entire galaxy, but only perhaps a few unlucky stars nearby.chaouki: Is it possible that a black hole can approach the earth?Jerry: Not very likely. We don't know of any very nearby black holes.Akarsh_Valsan: Who was Subrahamayan Chandrashekar?Jerry: A famous Indian-American astrophysicist at the University of Chicago. The Chandra X-ray Observatory was named for him. http://www.nasa.gov/chandra.longsheryl: How big are these black holes?Jerry: Black holes really don't have any size. They're called singularities and they have no dimensions. It's hard to imagine because we live in a 3-D world, and black holes are 4-D. (To clarify...we live in a 4-D world, but this can only be seen over extremely large distances.)Lester_Morgan: Do evaporating black holes produce gamma rays bursts?Jerry: No, the collapse of massive stars that form black holes are believed to produce gamma ray bursts.Fox: Will black holes still be around after the heat death of the universe?Jerry: Yes, the larger black holes will probably outlive the Universe.Elaine: How many black holes are in the Milky Way?Jerry: We think there are perhaps thousands of black holes in our own galaxy, but so far, we've only seen the ones that are in close binary systems, several dozen at most.chris_ryce: How far away from us is the nearest known black hole?Jerry: About 30,000 light years. This is Cygnus X-1.Akarsh_Valsan: Sir, are black holes left over from a supernovae?Jerry: Most supernovae are thought to form neutron stars. These have smaller masses than black holes and don't have singularities. The black holes are thought to form from hypernovae.Nazban: Hi Sir, is it true that quasars are the brightest objects in the universe? and they are powered by a black hole?Jerry: Yes, quasars are the brightest CONTINUOUSLY shining objects in the universe. However, gamma ray bursts briefly outshine quasars.bryte: Theoretically, what would make up a white hole?Jerry: "White holes" are controversial.digital: Are there any connections between gamma ray bursts and black holes?Jerry: We think that a gamma ray burst signals the birth of a black hole.ual8658: Is it possible for a black hole to suck up earth?Jerry: The Earth won't get sucked into a black hole because there are none that are thought to come close to us.simulacra: How are jets of radiation formed that shoot out of black holes if black holes have such huge gravity?Jerry: Material that's drawn near a black hole goes into orbit and it's thought that the combinations of circular motion and entrained magnetic field will cause it to shoot out as oppositely-directed jets from the black hole, overcoming even the gravity of the black hole.xbltheshadow: What is the closest Black Hole to Earth?Jerry: About 30,000 light years.celestialm00n: What is the relation with blackholes and dark matter? is there a possibility black holes feed black matter which is why it is expanding?Jerry: Most astronomers don't think that black holes would constitute enough matter to explain the dark matter that's seen.jocampo: Why is there a Black Hole in the middle of every Galaxy?Jerry: Most astronomers think it was formed in the very early stages of the formation of the galaxy when a group of stars coalesced.jocampo: What does the Scharzschield radius really tell us about Black Holes?Jerry: The Scharzschield radius has a very simple relationship to the mass of a black hole.rahulr96: If a black hole has no source of energy to drain will it quickly die out?Jerry: No, it can still live on.jpelch: Are there quasars near the Milky Way?Jerry: The nearest quasar was also one of the first ones to be discovered. It's known by its radio source name, 3C273.jocampo: How many solar masses is it required for a star to become a black hole?Jerry: Most astronomers believe that a black hole weighs a minimum of about 20X the mass of our Sun.rahulr96: What are black holes made of on the elemental level?Jerry: Black holes can't be described as being composed of any normal material, including molecules, elements, or elementary particles.Aperture_Science: Thanks for answering all our questions! =)Jerry: You are very welcome -- I appreciate these GREAT questions!