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  • [ ♪ Intro ]

  • Almost 14 billion years ago, the universe began with a big bang.

  • And while that was great and all, the real space news lately has been about what happened

  • around a quarter of a million years later.

  • By then, the newborn universe had finally cooled down enough for neutral, uncharged atoms to form.

  • And at some point, those atoms combined.

  • Specifically, helium atoms combined with charged hydrogen ions to make the very first molecule:

  • the helium hydride ion, called HeH+ for short.

  • Then, this molecule went on to shape the first stars and galaxies, and the rest is history.

  • Of course, this story was originally just based on our understanding of chemistry;

  • no one was actually there to see this happen.

  • And that led to a conundrum.

  • Because after decades of searching,

  • scientists had found no definitive evidence of helium hydride ions in space at all.

  • That is, until now.

  • In a paper published last week in the journal Nature, an international team has reported

  • that they have finally detected this elusive ion!

  • Now, to be clear, scientists knew that helium hydride ions could exist,

  • because they were created in the lab way back in 1925.

  • They just hadn't been found anywhere in interstellar space.

  • A big part of the reason is probably that is probably because these ions are incredibly reactive.

  • Helium hydride is the strongest known acid,

  • and it'll react with any other neutral molecule it encounters.

  • And a single electron will break it apart.

  • In fact, the only thing it won't react with is another positively-charged ion.

  • So we didn't expect this search to be easy.

  • Still, it's not like scientists were being unreasonable.

  • They weren't looking for the literal first molecules in the universe,

  • since those helium hydride ions are long gone.

  • Instead, they were studying places with conditions similar to that of the early universe,

  • and were trying to search for these ions there.

  • They even had the perfect place to look: the insides of planetary nebulas.

  • These are beautiful shells of gas cast off by dying stars,

  • and they typically surround a hot white dwarf star.

  • The white dwarf drives intense waves of radiation into the nebula,

  • which are strong enough to rip electrons from atoms and create huge regions of ionization,

  • where some interesting chemistry can take place.

  • It doesn't create exactly the same conditions as in the early universe,

  • but it's the closest we're likely to get.

  • One especially promising nebula has been NGC 7027, which is about 3000 light-years away.

  • This nebula is only around 600 years old, which means it's still really dense,

  • and its central star is one of the hottest we know of, burning at nearly 190,000°C.

  • With all that dense gas and extreme radiation, researchers have thought for a while that

  • this nebula would create the ideal conditions for helium hydride to form.

  • But recently, the problem hasn't been so much where to look for these ions

  • as how to actually see them.

  • Astronomers are normally able to detect molecules in space by tuning in to the characteristic

  • frequencies that they vibrate at.

  • The problem is, helium hydride vibrates the strongest at incredibly high frequencies

  • more than 2 Terahertz.

  • That puts its emissions in the far infrared part of the electromagnetic spectrum.

  • And while some of our space telescopes have been able to detect far infrared light,

  • they haven't been sensitive enough to distinguish helium hydride ions from similar molecules.

  • To make the situation even more complicated,

  • things like water vapor in the Earth's atmosphere are really good at absorbing infrared radiation,

  • so any instruments here on the ground are more or less useless.

  • But we did detect helium hydride ions.

  • And to do it, we used a great piece of cutting-edge tech onboard a flying observatory!

  • It's called GREAT, and it's a new, super sensitive receiver

  • able to detect vibrations at more than 2 Terahertz.

  • It was launched onboard SOFIA, a type of Boeing 747 jetliner

  • that NASA modified to carry an almost 3-meter telescope.

  • Even though SOFIA is still in the atmosphere, it flies more than 12 kilometers above the ground,

  • which is above most of the atmosphere's infrared-absorbing water.

  • Also, the good thing about using a plane instead of a satellite,

  • is that new detectors can easily be installed, without the need for expensive and risky rocket launches.

  • So GREAT was installed on SOFIA and linked to its telescope,

  • and together, they collected data from NGC 7027 for over an hour across three flights in 2016.

  • Then, the processed data confirmed what astronomers had hoped to find:

  • that clear spectral signature of the elusive helium hydride ion.

  • This detection has helped put everyone's mind at rest about what happened just after the Big Bang,

  • but that's not the only reason it's important.

  • It's also helping astronomers figure out how molecules form and are destroyed

  • in these heavily radiated environments.

  • And now that we have the tech to spot helium hydride ions in planetary nebulas,

  • we can really study it.

  • We can start to understand the processes from the dawn of chemistry in more detail.

  • Which is good news for scientists past and present and future!

  • Speaking of great news, if you love learning with us here at SciShow,

  • I think you'll probably enjoy our podcast.

  • It's called SciShow Tangents.

  • It's co-produced by me and my buddy Sam Schultz,

  • and created as a collaboration between Complexly and WNYC Studios.

  • It's hosted by Hank and Sam, along with Stefan Chin from the main SciShow channel

  • and Ceri Riley, who's a bonafide genius and writes for SciShow and Crash Course.

  • In every episode, these four show up with the most mind-blowing facts they can find about a topic

  • and try not to go on too many tangents, but even their tangents are really fun and interesting.

  • They also answer audience questions, make up science poems, and go head-to-head in Truth or Fail.

  • That's a segment where somebody presents two fake science facts and one real one,

  • and the other hosts have to figure out which one is the true fact.

  • Which is surprisingly difficult, because the made-up facts are very convincing.

  • Listening to SciShow Tangents feels like hanging out with your hilarious and super smart friends.

  • New episodes come out every Tuesday

  • and you can listen wherever and however you like listening to podcasts.

  • [ ♪ Outro ]

[ ♪ Intro ]

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科學家是如何發現宇宙中第一種分子的|科學秀新聞網 (How Scientists Found the First Type of Molecule in the Universe | SciShow News)

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    林宜悉 發佈於 2021 年 01 月 14 日
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