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by Fraser Cain
29 November, 2016
from
UniverseToday Website
When we do finally learn the full truth about our place in the
galaxy, and we're invited to join the
Galactic Federation of Planets, I'm
sure we'll always be seen as a quaint backwater world orbiting a
boring single star.
The terrifying tentacle monsters from the nightmare tentacle world
will gurgle horrifying, but clearly condescending comments about how
we've only got a single star in the Solar System.
The beings of pure energy will remark how only truly
enlightened civilizations can come from systems with at least 6
stars, insulting not only humanity, but also the horrifying tentacle
monsters, leading to another galaxy spanning conflict.
Yes, we'll always be making up for our stellar deficit in the eyes
of aliens, or whatever those creepy blobs use for eyes. What we lack
in sophistication, however, we make up in volume. In our Milky Way,
fully 2/3rds of star systems only have a single
star.
The last 1/3rd is made
up of multiple star systems.
The Milky Way
as seen from Devil's
Tower, Wyoming.
Image Credit: Wally
Pacholka
We're taking binary stars, triple star systems, even exotic 7 star
systems.
When you mix and match different types
of stars in various Odd Couple stellar apartments, the results get
interesting.
Consider our own Solar System, where the Sun and planets formed
together out a cloud of gas and dust. Gravity collected material
into the center of the Solar System, becoming the Sun, while the
rest of the disk spun up faster and faster. Eventually our star
ignited its fusion furnace, blasting out the rest of the stellar
nebula.
But different stellar nebulae can lead to the formation of multiple
stars instead. What you get depends on the mass of the cloud, and
how fast it's rotating.
Check out this amazing photograph of a multiple star system forming
right now.
ALMA image of
the L1448 IRS3B system,
with two young stars
at the center and a third distant from them.
Spiral structure in
the dusty disk surrounding them
indicates instability
in the disk, astronomers said.
Credit: Bill Saxton,
ALMA (ESO/NAOJ/NRAO), NRAO/AUI/NSF
In this image, you can see three stars forming together, two at the
center, about 60
astronomical units (AU) away from
each other (60 times the distance from the Earth to the Sun), and
then a third orbiting 183 AU away.
It's estimated these stars are only 10,000 to 20,000 years old. This
is one of the most amazing astronomy pictures I ever seen.
When you have two stars, that's a binary system. If the stars are
similar in mass to each other, then they orbit a common point of
mass, known as the barycenter.
If the stars are different masses, then
it can appear that one star is orbiting the other, like a planet
going around a star.
When you look up in the sky, many of the single stars you see are
actually binary stars, and can be resolved with a pair of binoculars
or a small telescope. For example, in a good telescope, Alpha
Centauri can be resolved into two equally bright stars, with the
much dimmer
Proxima Centauri hanging out
nearby.
The two bright stars
are
(left) Alpha Centauri
and (right) Beta Centauri.
The faint red star in
the center
of the red circle is
Proxima Centauri.
Credit: Skatebiker at
English Wikipedia (CC BY-SA 3.0)
You have to be careful, though, sometimes stars just happen to be
beside each other in the sky, but they're not actually orbiting one
another - this is known as an optical binary. It's a trap.
Astronomers find that you can then get binary stars with a third
companion orbiting around them. As long as the third star is far
enough away, the whole system can be stable. This is a triple star
system.
You can get two sets of binary stars orbiting each other, for a
quadruple star system.
In fact, you can build up these combinations of stars up. For
example, the
star system Nu Scorpii has 7 stars
in a single system. All happily orbiting one another for eons.
If stars remained unchanging forever, then this would be the end of
our story.
However, as we've discussed in other
articles, stars change over time, bloating up as red giants,
detonating as supernovae and turning into bizarre objects, like,
And when these occur in multiple star
systems, well, watch the sparks fly.
There are a nearly infinite combinations you can have here: main
sequence, red giant, white dwarf, neutron star, and even black
holes. I don't have time to go through all the combinations, but
here are some highlights.
This artist's
impression shows VFTS 352
- the hottest and
most massive double star system to date
where the two
components are in contact and sharing material.
The two stars in this
extreme system lie about
160 000 light-years
from Earth in the Large Magellanic Cloud.
This intriguing
system could be heading for a dramatic end,
either with the
formation of a single giant star or as a future binary black hole.
ESO/L. Calçada
For starters,
binary stars can get so close they
actually touch each other. This is known as a contact binary,
where the two stars actually share material back and forth.
But it gets even stranger...
When a main sequence star like our Sun runs out of hydrogen fuel in
its core, it expands as a red giant, before cooling and becoming a
white dwarf. When a red giant is in a binary system, the distance
and evolution of its stellar companion makes all the difference.
If the two stars are close enough, the red giant can pass material
over to the other star. And if the red giant is large enough, it can
actually engulf its companion.
Imagine our Sun, orbiting within the
atmosphere of a red giant star. Needless to say, that's not healthy
for any planets.
An even stranger contact binary happens when a red giant consumes a
binary neutron star. This is known as a
Thorne-Zytkow object. The neutron
star spirals inward through the atmosphere of the red giant. When it
reaches the core, it either becomes a black hole, gobbling up the
red giant from within, or an even more massive neutron star.
This is exceedingly rare, and only one
candidate object has ever been observed.
A Type Ia
supernova occurs
when a white dwarf
accretes material from a companion star
until it exceeds the
Chandrasekhar limit and explodes.
By studying these
exploding stars, astronomers can measure dark energy
and the expansion of
the universe.
CfA scientists have
found a way to correct for small variations
in the appearance of
these supernovae,
so that they become
even better standard candles.
The key is to sort
the supernovae based on their color.
Credit: NASA/CXC/M.
Weiss
When a binary pair is a white dwarf, the dead remnant of a star like
our Sun, then material can transfer to the surface of the white
dwarf, causing novae explosions.
And if enough material is transferred,
the white dwarf explodes as a
Type 1A supernova.
If you're a star that was unlucky enough to be born beside a very
massive star, you can actually kicked off into space when it
explodes as a supernova. In fact, there are rogue stars which such a
kick, they're on an escape trajectory from the entire galaxy, never
to return.
If you have two neutron stars in a binary pair, they release energy
in the form of gravitational waves, which causes them to lose
momentum and spiral inward.
Eventually they collide, becoming a
black hole, and detonating with so much energy we can see the
explosions billions of light-years away - a short-period gamma ray
burst.
The combinations are endless...
How Earth
could look with two suns.
Credit:
NASA/JPL-Caltech/Univ. of Ariz.
It's amazing to think what the night sky would look like if we were
born into a multiple star system. Sometimes there would be several
stars in the sky, other times just one.
And rarely, there would be
an actual night.
How would life be different in a multiple star system?
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