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In 2016, two Caltech astronomers proposed
that our solar system is home to nine planets.
And no, they didn't reclassify Pluto.
Instead, they found evidence for a hypothetical Neptune-sized planet
at least forty billion kilometers from the Sun
far enough that it would take fifteen thousand years for it to complete one orbit.
In the last three years, this Planet 9 hypothesis has continued to gain support.
But last week, two other scientists proposed
that this object could be something a little more exotic.
Instead of a planet out there, they say it could be a black hole,
but like...a tiny black hole.
Like, the size of your fist.
Like...a chihuahua's head!
This paper hasn't gone through peer-review yet, but it's making some big claims.
And one way or another, it could teach us more
about what's lurking in our solar system.
This whole Planet 9 thing came about after researchers noticed something strange
about the outskirts of the solar system.
There's a lot of small rocky and icy bodies out there,
and many of them have weird orbits.
Ones so weird that they seem to be affected by the gravitational pull of some larger,
unknown body - something between 5-15 times the mass of Earth.
If there's something out there, it's probably a planet,
but technically, any object with the right amount of mass would do.
Including a special kind of black hole.
Normally, black holes form from massive stars,
so they're millions of times heavier than the Earth.
But there's a hypothetical kind of black hole that could be much lighter
like, five to fifteen times the mass of our planet.
They're called primordial black holes,
and they may have been created shortly after the universe began.
At that time, everything in existence was packed close together.
And as the idea goes, primordial black holes formed
when extra dense pockets of matter collapsed in on themselves.
According to this new hypothesis, an object like this could have been captured
by the Sun's gravity, and it would easily explain
all the weird orbits we've seen past Neptune.
Now, since black holes are so dense, this thing would be small
only about nine centimeters across.
But it might still be easier to spot than a distant planet.
At least, if you don't rely on visible light.
Scientists believe that primordial black holes would be surrounded by halos of dark matter.
This is a type of matter we can't directly detect,
but that most evidence suggests is out there.
The authors of this paper argue that, occasionally, dark matter around the black hole
could interact with similar particles and turn into gamma radiation.
Lucky for us, we have telescopes that can pick that up.
So theoretically, if we started seeing gamma ray flashes out past Neptune,
it could be a sign that we have a local black hole.
This hypothesis is definitely in need of more evidence, but even if it doesn't pan out,
searching for a primordial black hole wouldn't be useless.
It would likely allow us to learn more about dark matter, primordial black holes,
and the flashes of gamma rays we've already detected.
So one way or another, it seems like a possibility worth investigating.
In other black hole news, because it's that kind of week,
a handful of telescopes has detected something super hardcore:
A black hole three hundred seventy-five million light-years away,
ripping apart a star with the power of gravity.
The results were published last week in The Astrophysical Journal.
The discovery itself happened in January,
and the first instrument to notice something going on was NASA's TESS.
TESS has been orbiting Earth for a little over a year now,
and it stares at one large section of sky for several weeks at a time.
Its main goal is to find planets beyond the solar system, but because it's just floating
around out there with its proverbial eyes open,
it's bound to observe other phenomena, too. And that's what happened last winter.
In January, the telescope picked up an increase in brightness coming from a distant star.
Then, several days later, less-sensitive instruments on the ground noticed the same thing.
The event came to be called ASASSN-19bt
after the first project to give us data about it.
Because even though TESS technically saw it first,
it only sends data to Earth every two weeks, so the other team got the naming rights.
This brightening turned out to be the early stages of a tidal disruption event, or TDE.
Which is a scientific way of saying a star is getting absolutely wrecked by a black hole.
The murderous culprit sits at the center of a galaxy called… okay, don't make me say that.
I don't know how to say that.
Look, you're never going to visit this thing.
The bigger point is that this black hole seems to be
about six million times more massive than the Sun.
That's fifty percent more massive than
the supermassive black hole at the center of the Milky Way.
The more mass an object has,
the more of a gravitational pull it has on the stuff around it.
So when a star wandered too close to this black hole, things got messy.
The difference in gravity between one side of the star and the other became so great
that it overcame the forces holding the star together.
In other words, the black hole ripped the star apart.
Some of the star's gas and plasma likely escaped into the void of space,
but the rest tumbled down toward the black hole,
creating a swirling disk and a large flare of radiation we could see from Earth.
Tidal disruption events are super rare, and scientists have only captured
about forty of them so far.
That means each new observation can teach us something.
In this case, observing the event early-on allowed researchers
to chart the extreme drop in the star's temperature that happened
within the first few days.
It went from forty thousand degrees Celsius to only twenty thousand.
Something like this was in our prediction models, but now we have actual evidence.
Scientists will continue to study this event, both with TESS and with other instruments.
And ultimately, their data will help them develop better models for how TDEs happen.
From tiny, hypothetical objects to monsters that rip apart stars,
there's a lot in the news about black holes this week.
But if these papers show us anything, it's that there's always more to learn.
Thanks for watching this episode of SciShow Space News!
Before you go, I have an update for you!
Every month, we release a new, space-themed pin,
and October's pin is officially available!
It's of Sputnik, humanity's first artificial satellite,
and it's very, very good and shiny and fun.
And you can only get it during the month of October, so if you're interested,
check out the link in the description or the merch shelf below the video.


Planet 9 Could Be a Black Hole?! | SciShow News

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林宜悉 2019 年 11 月 4 日 に公開
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