Can Black Holes Eat One Another?

Question: Ok so say the universe gets to a point where every black hole consumes everything including each other until your left with a single black hole. Or would this not be possible due to the universe ever expanding and just the vastness of the universe ? Just a thought.  – Danny

Answer: Space is actually a pretty empty place on average.  The WMAP cosmic microwave background probe measurements indicated that there are on average about 6 protons per cubic meter in the Universe.  I believe therefore that the possibility of black holes even interacting with each other is pretty small.

Jeff Mangum

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What are the Effects on Radio Waves When They Pass Near a Black Hole?

Question: What are the effects of radio waves when near a black holes event horizon?  – Aleksander

Answer: Assuming that you are asking what the effects of a black hole are on radio waves as they pass near an event horizon, these effects would be the same as those experienced by all electromagnetic waves.  Since the gravitational field near a black hole is “warped” by the intense gravitational field of the black hole, electromagnetic waves at all wavelengths, including radio waves, would be “bent” by this intense gravitational field.

Jeff Mangum

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What Happens to Matter that Falls into a Black Hole?

Question:  So a question from the uneducated. If all matter at the beginning was in one infinitely small point so incredibly charged with energy would that weight punch through space creating a hole in the universe  thus creating the first black hole perhaps the backlash of the initial tearing of space created such an explosion that the matter known and still unknown is the blowback from such an immense explosion?  Also does a black hole act like a tunnel through space or the inbetween space  dumping its matter out in nonspace slowly filling the nonspace with matter or does it tear through another location in space erupting the energy into space thus recycling the the energy?  Or is a black hole an infinitely deep pit in the space as we know it and just continuously sucking in all matter and energy?  – Sean

Answer:  Based on current accepted theory of the structure of black holes all we can say is that matter eventually falls onto the singularity, or point where the gravitational force is infinite, and is therefore compressed to a single point.  Your last suggestion is the one most consistent with what theorists believe is the structure inside a black hole.  As you can probably imagine, it is very hard to obtain measurements of black holes that we can use to better constrain these theories, making them rather open to interpretation.

Jeff Mangum

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How Can a Black Hole Have an Outflow?

Question:  Black holes are defined as a zone where the gravity is so dense that nothing, not even light, can escape from being drawn in, yet “Fermi Bubbles” are where ” energy often escapes from these systems (Galaxies ) in a jet”.  This sounds like a contradiction.  Is there an explanation?  – Stephen

Answer:  The Fermi bubbles are two large gamma-ray structures in located above and below the Galactic center.   At the moment there are several theories as to the origin of these bubbles, including past dynamical processes that resulted in large amounts of gas being pushed into these regions.  The most plausible dynamical process would be the outflow from a supermassive black hole.  Even though black holes swallow matter as it orbits in a disk-like structure around the black hole, a small fraction of that matter escapes vertically via an outflow of material, a consequence of the need for the black hole plus disk system to conserve angular momentum.  So, in fact, a black hole system can produce both an inward and outward flow of matter.

Jeff Mangum

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Can One Send a Spacecraft Into a Black Hole?

Question:  [Would it be possible to] send a spacecraft into a black hole?  – Cyrus

Answer:  Yes, but if we were to do that we should make sure to use one of our least expensive spacecrafts!  And there better not be any astronauts in the spacecraft.  This is all because when something enters a black hole it can never come out.  The spacecraft would be gobbled up by the black hole never to be seen from again.

Jeff Mangum

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Can Black Holes Explode?

Question:  Can a black hole explode?  – Dirk

Answer:  Black holes don’t really “explode”, which implies that they generate a large outburst of energy which ultimately tears them apart, but they do have outbursts (also, unfortunately, referred to as “explosions”).  The black hole at the center of our Galaxy, for example, appears to have produced an outburst of energy about two million years ago.

Jeff Mangum

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Can Gravitationally-Lensed Objects be Studied at Any Wavelength?

Question:  As per definition, Gravitational lensing refers to bending of light rays from a distant source around a massive object (Galaxy cluster) which tends to magnify the background light source. If visible light rays bend around those massive objects then X-rays, Gamma rays, UV and IR rays which forms a part of electromagnetic spectrum must also bend around those massive objects. If true, Are there any initiative to detect those distant lensed invisible objects using the space observatories(Chandra X-ray, Spitzer IR etc.)?  – Vinod

Answer:  Yes.  In fact, just a few days ago there was a press release announcing the detection of the spin of a black hole using the gravitationally-lensed x-ray emission from a black hole in a distant quasar.  Gravitational lensing has also been used to study galaxies using the Spitzer Space Telescope.  In fact, as their is no wavelength dependence to the gravitational lens effect it is possible to study gravitationally-lensed objects at all wavelengths.

Jeff Mangum

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What is the Critical Mass at Which a Star Becomes a Black Hole?

Question:  How do you calculate the critical mass for a star to become a black hole? I’m an undergraduate Math major, and this is my senior thesis and I really have no idea where to start.  – Lauren

Answer:  An earlier post to this blog on “Properties of Stars which Result in Black Holes” provides a general overview to this question.  Since the exact mass of an object like a star that must ultimately become a black hole is a function of its radius, there isn’t an exact mass above which that object must collapse to a black hole.  Said another way, any object which collapses to the point where its radius is less than a certain limit must ultimately become a black hole.  This radius is called the Schwarzschild radius (Rs), and it is given by the following equation:

Rs = 2MG/c^2

where M is the mass of the object, G is the gravitational constant, and c is the speed of light.  If you plug in values for the constants G and c and use solar masses for M and km for Rs, this equation reduces to the following rather simple form:

Rs = 2.95*M(solar masses) km

So, for a star with the same mass as our Sun, the Schwarzschild radius is about 3 km, or about 2 miles.  In general, stars with final masses in the range 2 to 3 solar masses are believed to ultimately collapse to a black hole.

Jeff Mangum

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Top Achievements for the NRAO Very Large Array

Question:  I’m embarrassed to ask this, as I feel after working here for so long I should already know the answer. But here it is: What are the top 3 discoveries/achievements of the VLA? And why?  — Doug

Answer:  As you can imagine, an actually ranking of the Very Large Array (VLA) achievements would be open to debate.  Kind of “beauty in the eye of the beholder” problem.  Dave Finley, NRAO Public Information Officer, provided the following links listing what NRAO believes are the VLA’s top scientific achievements:

Jeff Mangum

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Will Dark Energy Tear Apart Black Holes?

Question:  Will dark energy eventually tear apart black holes, especially supermassive black holes?  – Reinaldo

Answer:  Let’s start with a basic understanding what what Dark Energy is thought to be.  It is a hypothetical form of energy which is thought to pervade the universe.  It has been proposed as the source of the measured acceleration of the expansion of our universe.  As a physical entity it is really quite “thin”, having a density of about 10^(-29) grams per cubic centimeter, so its affect of things like planets, stars, humans, and black holes is exceedingly small.  But, because it is thought to fill the universe its affect on the expansion of the universe is very important.  So, to answer your question, Dark Energy does not affect the properties of black holes, so in fact cannot disrupt them in any way.

Jeff Mangum

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