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{♫Intro♫}
Stars explode and die all the time, but they're so faint and far away that on Earth, we rarely
notice.
Dying stars we can see with the naked eye are few and far between.
Luckily for us, though, three astronomers announced at the American Astronomical Society
meeting last week that in not too long, we're in for a treat.
They found that, as early as the 2060s, two stars are going to merge, and that event will
be so bright that we'll be able to see it with the naked eye!
The 2060s might seem like a long way off for us mere mortals, but it will definitely be
spectacular.
Because this explosion won't be your typical supernova.
It will be something completely new to us.
The system is called V Sagittae.
It's roughly 7800 light-years from here, and it's classified as a Cataclysmic Variable,
or CV.
That means it's a binary star system made of a relatively Sun-like star and a white
dwarf.
That's the leftover core of a star that wasn't massive enough to undergo a supernova
at the end of its life.
And these two objects are close enough that the white dwarf's gravity pulls matter off
its companion, stealing it and gaining mass as a result.
In normal cases, these systems are mind-boggling.
Because eventually, the gluttonous white dwarf will steal so much matter that it either explodes,
or its outer layer gets blasted into space.
But V Sagittae is special.
It's the only CV we know of whose white dwarf is less massive than its companion.
About four times less massive, too.
This imbalance causes some weird effects, but ultimately, it means the stars in this
system aren't in a stable orbit.
They're spiraling toward each other, and eventually, they're going to collide.
Recently, this team analyzed data about the system's light and position going back to
1890.
And they confirmed V Sagittae is in the middle of this death spiral, and that somewhere between
2067 and 2099, the two objects will officially merge.
That will create a new light in our night sky for more than a month!
Right now, this system is too dim to be visible.
But during that month, it will be as bright as Sirius — the current brightest star we
can see after dark.
And it could even briefly be as bright as Venus, the brightest night-time object besides
the Moon — or the International Space Station, depending on the timing.
When it's all over, this system will end up as a single star, and it's not clear
if we'll be able to see it without a really fancy telescope.
So most of us might not have long to see this for ourselves.
But whatever time we /do/ have will still be amazing.
Of course, while 80 years is barely a blink of an eye on cosmic time scales, 2099 is pretty
far away…
So, here's hoping that merger happens sooner rather than later.
Because, let's be honest: I'd really like to be around to see it.
While we wait for the future to arrive, though, let's take a moment and look back to the
past.
Because this Monday in the journal PNAS, scientists announced the oldest solid matter ever found
on Earth.
It's a compound called silicon carbide, and it formed hundreds of millions of years
before our solar system was born.
And, as if that weren't cool enough, it also gives astronomers some clues about our
galactic history.
Most of the solids in our solar system — things like dust and rocks — condensed from gas
about 4.6 billion years ago, about the time the Sun formed.
But a tiny percent of dust was already there, just hanging out.
Astronomers call them presolar grains, but you'll sometimes hear the more poetic term
“stardust”.
That's because they formed in the outer atmospheres of red giant stars in the last
stages of their lives.
As the stars died and shed their outer layers, the grains entered interstellar space and
got struck by cosmic rays — high-energy, charged particles.
That caused reactions that changed the elements the grains were made of.
Eventually, these tiny pieces wandered into our neighborhood.
When our solar system started forming, some of them got encased by new solid matter, which
protected them against further damage and the effects of time.
While a lot of that matter went on to form planets, plenty was left over, free to hit
Earth in the form of meteorites.
And so, billions of years later, we've started finding them.
Presolar grains are really rare and tiny — typically a few millionths of a meter in size.
But they do turn up.
The meteorite containing these record-breaking grains landed in Australia back in 1969.
And recently, scientists took a fragment of that space rock, crushed it up, and used acid
to dissolve all but the silicon carbide grains.
Then, they calculated the age of those grains by measuring how much of a special isotope
of neon they contained.
That amount determined how long the grains had been exposed to cosmic rays before getting
sealed up.
Most of the pieces had traveled through space for less than 300 million years before being
incorporated into the early solar system.
So, that would put them around 4.9 billion years old at most.
But a few other pieces had traveled for more than a billion years.
Making them more than 5.5 billion years old.
It's those little guys that set the record for the oldest solids on the planet.
But don't get me wrong: Those younger grains are important, too.
Their abundance supports the hypothesis that our galaxy's production of stars isn't
constant.
That there was a surge in star formation about seven billion years ago that produced the
stars needed to create these grains.
And that's important, because researchers are still trying to figure out what star formation
has looked like over time.
And these grains could help them learn more.
So it's nice to know you can be important without having to break records.
Excellent motivational message, universe!
Thanks for watching this episode of SciShow Space News!
Before you go, we wanted to let you know that our pin of the month is currently available!
This month, it's celebrating Explorer 1, the first satellite the U.S. ever launched
into space!
We've come so far.
The pin is pretty rad, but it's only available during the month of January — so if you
want one, you've only got a couple weeks left.
To check it out, you can go to DFTBA.com/scishow or find the pin in the merch shelf below.
Thanks
{♫Outro♫}
コツ:単語をクリックしてすぐ意味を調べられます!

読み込み中…

Get Ready for a New Star in the Night Sky! | SciShow News

林宜悉 2020 年 2 月 17 日 に公開
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