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Answers To Your Questions On Black Holes

Our Monday, March 2, 2015 hour on surprising new discoveries on black holes lead many of you to ask some pretty expansive questions on our website during and after the show. We couldn't answer them all (and we really couldn't — we had to turn to our expert guests for that) but  Priyamvada Natarajan, professor of astronomy and physics at Yale University, offered to answer some of your questions on black hole science and mystery here.


 Beetlegues is 600 light years away from us.  Will Beetlegues turn into a black hole after it explodes?

The mass of Betelguese is 7.7 times the mass of the sun. So upon exhausting burning all the hydrogen that is powering the star it will eject the outer envelope as a planetary nebula and then leave behind a white dwarf star. Alas! this one will not explode and leave a black hole behind.

We can see stars, planets, nebula, comments, satellites with the naked eye.  Can't see black holes with the naked eye?

First of all, we can only see astronomical objects that are either very close by or incredibly bright with the naked eye. For example, we see comets only when they swing by real close, for most of the time that comets are whizzing around, we dont see them. There are no black holes close enough that we can see the gas swirling into it by naked eye.

The nearest black hole to us is the one in the center of the Milky Way and that is 100,000 light years away.

What happens when one black hole reaches another?

When two black holes get real close and collide they merge together and form a bigger more massive black hole. The dying gasps of these colliding black holes releases gravitational radiation. Here is a link to a movie from a simulation of what happens with two black holes merge.

With this discovery what kind of upward limit can we put on the size of a black hole now and what effect does this object have on the space around it?

Well there is scientific work on how the upper limit can be estimated for black holes at any given cosmic epoch. As for the impact of the black hole on spacetime - take a look at this artists' impression. Black holes cause a puncture in spacetime as opposed to gentler bumps that less compact objects like our Sun create.

This is sooooooo much bigger than our sun, which is already beyond our capabilities to appreciate its size. What else might be lurking in the cosmos that hasn't been spotted yet???

Exactly! these sizes and scales are so unfathomable to us given our daily experience. Who knows what kind of exotic object is lurking out there in deep space waiting for us to discover it.....

The guests say that black holes exist. But are the real or are they just a name given to what we can observe, and explain using the physics we know.

Well, they are real as in that we detect the indelible impact they have around them. Black holes exist as their intense gravity (that warps the space-time fabric around them) affects the motions of stars and gas in their vicinity and additionally they also cause the bending of light. All of these impacts that they make are observed - we have empirical data and evidence. Take for instance this movie of the motions of the stars at the center of the Milky Way.

Is there any evidence or example of the other end of a black hole within our universe?

No there is no current evidence for a wormhole, empirical evidence that is, although it is mathematically allowed.

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