
Astronomers may have witnessed a star torn apart by a black hole - wglb
http://blogs.discovermagazine.com/badastronomy/2011/04/05/astronomers-may-have-witnessed-a-star-torn-apart-by-a-black-hole/
======
GvS
Here is followup:
[http://blogs.discovermagazine.com/badastronomy/2011/04/07/fo...](http://blogs.discovermagazine.com/badastronomy/2011/04/07/followup-
on-the-star-torn-apart-by-a-black-hole-hubble-picture/)

------
JacobAldridge
This occured just on two weeks ago, for definitions of two weeks that
encompass plus or minus 4 billion years.

~~~
delinka
Is this not yet a Well-Known Fact that astronomers say "we observed it two
weeks ago" and We The Laymen know that Great Distances are involved and the
event itself happened "long, long ago, in a galaxy far, far away?"

~~~
robryan
Something I have wondered before, if we lived in a universe in which an
observation from essentially any distance was observable near instantaneously
would this help or hinder astronomy?

~~~
nopassrecover
I would say hinder. If we assume that interesting events are distributed
equally throughout space (i.e. the universe is uniform) but differ over time
(the early universe was obviously different to the current universe) then
astronomers currently get to observe a wide range of events throughout both
space and time. If events were observed immediately from all distances, then
astronomers would only be able to observe current events.

~~~
Deestan
On the other hand, it would be possible to effectively communicate with
distant species, who in turn might have existed for a long time and have
records of past events.

~~~
Dn_Ab
We would also be able to receive messages from distant species before they
sent them.

------
mryall
I was confused about which were actual images taken of the star and black
hole. The first one looks like an "artist's impression" - is it just the
grainy picture at the end which actually captures it?

------
portman
IANAA (I am not an astrophysicist) but isn't the accompanying image very
different from what actually happens when a star crosses the event horizon of
a black hole?

I thought that when an object crosses the event horizon of a black hole, to an
observer outside the event horizon, it will look like the object just slowed
down and sort of "suspended" there. I didn't think it would emit a burst of
radiation.

(This is just from reading Brian Greene and Michio Kaku, so my understanding
could be way off the mark.)

~~~
lincolnq
I think you may be confusing the event horizon with the Roche limit. The event
horizon is the distance where not even light can escape. The Roche limit is
the closest a body can come to another (more massive) body such that it can
stay intact with itself, as opposed to being torn apart by tidal forces in the
massive object's gravitational field.

I suspect, but do not know for sure, that the Roche radius for a black hole
and regular star is much larger than the event horizon for the same black
hole.

~~~
Retric
They are actually somewhat independent. The Roche limit depends on both body's
mass and volume, where the event horizon relates to a single body mass and
volume.

EX: Cold Brown dwarfs can orbit closer together than a brown dwarf and a earth
like planet.

PS: _Some real satellites, both natural and artificial, can orbit within their
Roche limits because they are held together by forces other than gravitation.
Jupiter's moon Metis and Saturn's moon Pan are examples of such satellites,
which hold together because of their tensile strength._

~~~
bfe
Basically correct (except the concept of volume doesn't hold up in a black
hole). It is theoretically possible to have a black hole big enough that its
Roche limit is inside its event horizon; but a black hole that big is probably
at least vanishingly rare in the observable universe.

~~~
Retric
A black hole has a volume less than it's event horizon. So, it's not really
undefined as much as ill defined. Also, a black hole's event horizon is not
necessarily a perfect sphere ex: two black hole's orbiting each other.

