Hello Space Lab.
I'm Maryam Modjaz.
I'm the assistant professor of astrophsyics
at the Center for Cosmology and Particle Physics
at New York University.
And I'm here to answer your questions.
The first question is:
If you are standing near the event horizon of a black hole
and someone pointed a beam of gamma rays at you,
would they remain gamma rays or turn into something else?
The short answer is that the gamma rays will turn into light
that has longer wavelengths, for example, radio waves.
And that has to do with an effect that happens near black holes
where gravity is very extreme.
So if you imagine gravity
as a rubber sheet around a massive object
that space then will be dented
and when you have light that's trying to climb out,
out of that dent, it becomes light at a longer wavelength.
That's called "gravitational redshift,"
something that Einstein theorized in the 1920s
and for which we have a lot of evidence.
So in summary, the light that would be shown
near the event horizon of a black hole
will no longer remain gamma rays,
but will be light at longer wavelengths,
for example, radio waves.
The second question is:
In about three billion years,
the Milky Way and Andromeda Galaxy will collide.
When that happens, would it affect the size of the black holes
in the centers of the two galaxies?
Would the two black holes band together to create a bigger one?
Most likely, yes.
When Andromeda and the Milky Way collide,
their central supermassive black holes
will, most likely, also merge
and create a larger, supermassive black hole.
We know that our own galaxy has a supermassive black hole
of around 4 million solar masses,
but we are not fully certain if also Andromeda
has a similar black hole and how its mass is,
how big its mass is.
So given some of the uncertainties and some of the work
that people are doing, though it does look very likely
that at around 4 billion years
during the merger of the two galaxies,
the central supermassive black holes
will create a larger supermassive black hole
and the two galaxies will create a new galaxy
which is more elliptical compared to the galaxies we have now
which are more spiral galaxies.
So you might be wondering what might happen
to our own solar system once the Milky Way and Andromeda collide.
Will our sun be colliding with another star
from the Andromeda galaxy?
Well the answer is no.
It turns out distances between stars are huge.
So our next star, our neighbor star
is around four light-years away.
And during the collision of the two galaxies,
our own solar system will stay intact.
Our own sun will not collide with another star.
But our solar system might have a different orbit
in this new galaxy.
And the natural consequence
of the collision between the Milky Way and Andromeda
will be that our night sky will be very different.
We will not be seeing a band of the Milky Way
as we're doing now,
but the whole sky will be filled
with stars from our own Milky Way
as well as from Andromeda Galaxy.
The final question is:
If a planet was orbiting a binary star
and traversed between the two stars
would it be ripped apart?
If so, what would the experience be
if you were standing near the fracture?
That's a very interesting question.
The short answer is that nothing much will happen.
The gravitational forces acting on that planet
will be there by the two stars,
but in most likelihood, it will not be so strong
as to fracture anything.
And we actually believe, we astronomers actually believe
that it's very hard to form a planet that would then traverse
between the two stars.
The exoplanets astronomers have found,
the three cases so far,
they have planets that orbit the double star system,
but do not traverse between the two stars.
Planets form by stuff that's very small sticking together
to make bigger things.
And then gravity can start acting and more stuff can adhere to it
because of gravity.
It's really hard to grow a planet
out of stuff that's moving between two stars
because the stuff will feel
the forces of gravity of those two stars.
These were all great questions.
If you have more questions you want to ask the next expert,
please leave them in the comments below.