Nothing can escape gravity. Not a moon, not a planet and not even light. That’s what
Black holes are a spot where gravity’s pull is huge, ending up being dangerous for anything that accidentally strays by.
But
how did black holes come to be, and why are they important? Below are 9
facts about black holes just a few tidbits about these fascinating
objects.
Fact 1: You can’t directly see a black hole.
Because
a black hole is indeed “black” — no light can escape from it — it’s
impossible for us to sense the hole directly through our instruments, no
matter what kind of electromagnetic radiation you use (light, X-rays,
whatever.) The key is to look at the hole’s
effects on the nearby environment, points out
NASA.
Say a star happens to get too close to the black hole, for example. The
black hole naturally pulls on the star and rips it to shreds. When the
matter from the star begins to bleed toward the black hole, it gets
faster, gets hotter and glows brightly in X-rays.
Fact 2: Look out! Our Milky Way likely has a black hole.
A
natural next question is given how dangerous a black hole is, is Earth
in any imminent danger of getting swallowed? The answer is no,
astronomers say, although there is probably a huge supermassive black
hole lurking in the middle of our galaxy. Luckily, we’re nowhere near
this monster — we are about two-thirds of the way out from the center,
relative to the rest of our galaxy — but we can certainly observe its
effects from afar. For example: the European Space Agency says
it’s four million times more massive than our Sun, and that it’s surrounded by surprisingly hot gas.
Sagittarius
A in infrared (red and yellow, from the Hubble Space Telescope) and
X-ray (blue, from the Chandra space telescope). Credit: X-ray:
NASA/UMass/D.Wang et al., IR: NASA/STScI
Fact 3: Dying stars create stellar black holes.
Say
you have a star that’s about 20 times more massive than the Sun. Our
Sun is going to end its life quietly; when its nuclear fuel burns out,
it’ll slowly fade into a white dwarf. That’s not the case for far more
massive stars. When those monsters run out of fuel, gravity will
overwhelm the natural pressure the star maintains to keep its shape
stable. When the pressure from nuclear reactions collapses,
according to the Space Telescope Science Institute,
gravity violently overwhelms and collapses the core and other layers
are flung into space. This is called a supernova. The remaining core
collapses into a singularity — a spot of infinite density and almost no
volume. That’s another name for a black hole.
Fact 4: Black holes come in a range of sizes.
There are at least three types of black holes,
NASA
says, ranging from relative squeakers to those that dominate a galaxy’s
center. Primordial black holes are the smallest kinds, and range in
size from one atom’s size to a mountain’s mass. Stellar black holes, the
most common type, are up to 20 times more massive than our own Sun and
are likely sprinkled in the dozens within the Milky Way. And then there
are the gargantuan ones in the centers of galaxies, called “supermassive
black holes.” They’re each more than one million times more massive
than the Sun. How these beasts formed is still being examined.
A binary black hole system, viewed from above. Image Credit: Bohn et al. (see
http://arxiv.org/abs/1410.7775)
Fact 5: Weird time stuff happens around black holes.
This
is best illustrated by one person (call them Unlucky) falling into a
black hole while another person (call them Lucky) watches. From Lucky’s
perspective,
Unlucky’s time clock appears to be ticking slower and slower. This is in accordance with Einstein’s theory of general relativity, which (simply put) says that
time is affected by how fast you go,
when you’re at extreme speeds close to light. The black hole warps time
and space so much that Unlucky’s time appears to be running slower.
From Unlucky’s perspective, however, their clock is running normally and
Lucky’s is running fast.
Fact 6: The first black hole wasn’t discovered until X-ray astronomy was used.
Cygnus
X-1 was first found during balloon flights in the 1960s, but wasn’t
identified as a black hole for about another decade. According to
NASA,
the black hole is 10 times more massive to the Sun. Nearby is a blue
supergiant star that is about 20 times more massive than the Sun, which
is bleeding due to the black hole and creating X-ray emissions.
Illustration of Cygnus X-1, another stellar-mass black hole located 6070 ly away. (NASA/CXC/M.Weiss)
Fact 7: The nearest black hole is likely not 1,600 light-years away.
An
erroneous measurement of V4641 Sagitarii led to a slew of news reports a
few years back saying that the nearest black hole to Earth is
astoundingly close, just 1,600 light-years away. Not close enough to be
considered dangerous, but way closer than thought. Further research,
however, shows that the black hole is likely further away than that.
Looking at the rotation of its companion star, among other factors,
yielded a 2014 result of
more than 20,000 light years.
Fact 8: We aren’t sure if wormholes exist.
A
popular science-fiction topic concerns what happens if somebody falls
into a black hole. Some people believe these objects are a sort of
wormhole to other parts of the Universe, making faster-than-light travel
possible. But as this
Smithsonian Magazine article points out,
anything is possible since we still have a lot to figure out about
physics. “Since we do not yet have a theory that reliably unifies
general relativity with quantum mechanics, we do not know of the entire
zoo of possible spacetime structures that could accommodate wormholes,”
said Abi Loeb, who is with the Harvard-Smithsonian Center for
Astrophysics.
Diagram of a wormhole, or theoretical shortcut path between two locations in the universe. Credit: Wikipedia
Fact 9: Black holes are only dangerous if you get too close.
Like
creatures behind a cage, it’s okay to observe a black hole if you stay
away from its event horizon think of it like the gravitational field
of a planet. This zone is the point of no return, when you’re too close
for any hope of rescue. But you can safely observe the black hole from
outside of this arena. By extension, this means it’s likely impossible
for a black hole to swallow up everything in the Universe (barring some
sort of major revision to physics or understanding of our Cosmos, of
course.)
