Before the advent of telescopes,
stars just appeared to be twinkling specks in the sky,
but all looked kind of similar.
But when we started attaching cameras to our telescopes,
a zoo of unusual suns with orbiting planets
and sister stars and lives ending in black holes
began to appear.
Here are some of the most unusual
and sought after stars in the universe.
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Located in the Scutum constellation,
UY Scuti is the largest star ever discovered.
This red giant spans a width 1,700 times
the diameter of our sun.
You wouldn't even be able to see the sun at this scale.
So if we place the UY Scuti at the center of our solar system,
it would engulf the entirety of Jupiter's orbit,
including the inner planets, the asteroid belt, the Earth.
It's that enormous.
Though it's the largest known star by volume,
its density is 3,000 times less than Mars's thin atmosphere.
It's not the brightest nor most massive nor hottest known star.
In fact, red giants are typically
pretty cool as star temperatures go.
UY Scuti was discovered in 1860, but when astronomers reexamined
it in 2012, it set the record for largest known diameter.
Did I mention it's big?
J0523, for short, is the smallest star ever discovered
and possibly the smallest star in existence.
This red dwarf star is located 40 light years away
in the southern constellation of Lepus, which is pretty close.
But it's so small and dim that you still
need a telescope to see it.
Shining a mere 8,000th the luminosity of the sun,
this star is smaller than Jupiter.
It's dim and tiny.
But could you go smaller?
Could you have a star that fits in the palm of your hand?
Well, no.
It wouldn't have enough mass to ignite the core
and start fusion.
That's what separates a star from the objects just lighter
than it-- the brown dwarfs.
J0523 appears to be at the limit of fusion, which
we think is around 1/13 the mass of the sun,
making it theoretically the smallest possible star.
Nicknamed the Black Widow Pulsar,
this unusual star was discovered in 2012.
A pulsar is a special type of neutron star.
That is a star that has collapsed under its own gravity
after a supernova explosion until it
is so dense that the neutrons it's composed of
are basically touching.
But there's more to a pulsar like J1311.
They are spinning very fast.
When you blinked just now, J1311 spun around 150 times.
What makes this pulsar so special is that it's not alone.
Orbiting at a distance of less than a round trip to the moon
is a small companion star 10 times the mass of Jupiter.
This pulsar is called a black widow binary,
because the pulsar is killing off its companion.
J1311 blasts away material from the smaller start as it
orbits every 93 minutes.
That's less time than you'll probably spend on email today.
And as it does so, the companion star
get smaller and smaller, until eventually, J1311
will be alone.
This is the oldest star ever discovered.
SM0313, for short, is located in the halo of the Milky Way
and thought to be close to the age of the universe itself.
How do we know that it's so old?
Well, the very first generation of stars
were made out of the only elements that
were around after the Big Bang-- hydrogen, helium, and lithium.
These stars where massive, tens or hundreds of times the sun's
mass, and the bigger a star, the shorter it lives.
So they exploded in supernovas spewing heavy metals
into the universe.
The second generation of stars incorporated some
of these heavy elements when they formed, and they
were likely smaller, so they could live to the present day.
Later generations of stars would contain even more heavy metals
as more stars went supernova.
SM0313 has the lowest abundance of heavy metals of any star
we've ever discovered.
But according to Professor Anna Frebel,
we don't know exactly how old it is.
Frebel is one of the astronomers researching
the star and my former advisor.
She's been searching for these relic stars
throughout her career and was able to age
a previous record holder, HE1523,
to about 13.2 billion years old, because it
has uranium, which astronomers can use to date stars.
But SM0313 has little to no uranium,
making it currently impossible to age.
All we know is that the star likely formed only a few
hundred million years after the Big Bang.
Imagine this.
A giant star explodes, leaving behind a super dense neutron
star.
Then this neutron core collides with a super giant star,
which absorbs the core to form a hybrid star.
It's a star packed into the shell of another star
like the turducken of stars.
Wait-- ducken.
This unusual object is called a ThorneZytkow Object
and was hypothesized in 1977 by Kip Thorne and Anna Zytkow.
In 2014, astronomers discovered HV2112
in the small Magellanic cloud.
It's the strongest candidate yet for this type of object.
ThorneZytkow objects could form either
when in a binary star pair, one star goes supernova and throws
off the balance, or in a crowded super cluster of stars.
On the outside, the star would look the same
as a bright red super giant, but the inner signature
would have other heavy elements like rubidium,
strontium, yttrium, zirconium, molybdenum, and lithium.
Sure enough, HV2112 has this chemical signature.
We can't say for sure that it's a hybrid star,
because new models are needed.
But it's a very promising candidate.
Thank you so much for watching.
I hope you enjoy the material in this video, and if you did,
check out Phil Plait's video on crash course
astronomy about stars.
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