ベテルギウスが暗くなったという話題

Kouji Ohnishi 大西浩次 @koujiohnishi

(1) ベテルギウスが超新星爆発とすると、どのように見えるのだろうか。超新星爆発のスタートは、中心核の重力崩壊だ。重力崩壊を始めてわずか数秒で中心核が潰れてしまう。この時、大量のニュートリノが放出される。この様子は、スーパーカミオカンデなどで検出されるに違いない。 pic.twitter.com/vAl9Ln3iOo

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Kouji Ohnishi 大西浩次 @koujiohnishi

(2) まさに、可視光で光り始める数日前にキャッチできるのだ。この時に、もし、非対称的に潰れると重力波は放出される（球対称なら受からない）。重力崩壊により発生した衝撃波が星の中を数日掛けて通過してゆく。 pic.twitter.com/g1vOhM5ccg

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Kouji Ohnishi 大西浩次 @koujiohnishi

(3) 2日後には、X線で輝き始め、衝撃波が星の表面に達した段階で高温の外層が青白く光り始めるはずだ。ベテルギウスまでの距離は600光年、マイナス10.5等星（半月）ほどの明るさで100日ほど輝き続け、その後次第に暗くなってゆく。 pic.twitter.com/US7mEFzVXa

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Kouji Ohnishi 大西浩次 @koujiohnishi

(4) ところで、私たちは、この瞬間に立ち会えるだろうか。ベテルギウスは、赤色超巨星であり、いつ超新星爆発が起きてもおかしくない状態である。そして、干渉計技術の向上で、ベテルギウスの半径が15年間で15％も縮んだ とか、表面がでこぼこの形になっている事などが判っている。 pic.twitter.com/IFG16AWQa6

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Kouji Ohnishi 大西浩次 @koujiohnishi

(5) しかし、これらの観測事実を超新星爆発の前兆現象だと断定することはできない。すなわち、2012年に爆発するという噂は「デマ」であった。また、たとえベテルギウスが爆発したとしても、地球への影響はないと考えられている。 pic.twitter.com/xHiB0mH6Rh

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Kouji Ohnishi 大西浩次 @koujiohnishi

(6) ただ、もし、爆発したら、冬のダイヤモンドの中央に青白くまぶしく輝き、次第に赤色に変化してゆく姿を数年間に渡り見ることができる。是非とも見たい光景ではあるが、オリオンの肩が無くなるのは寂しい気もする。 pic.twitter.com/aL4QH8G5YY

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Victor 🌌 @victor_astro

Today, I saw that a lot of astronomers/astrophysicists were talking about #Betelgeuse . Indeed, according to many, Betelgeuse luminosity seems to be quite low. Some say it’s extraordinary, others say it happens quite often, but all (secretly or not) hope for a supernova. 1/7

Victor 🌌 @victor_astro

Even if I don’t believe it is likely that a supernova will happen in the next weeks, I wanted to know if this dimming was actually extraordinary. I looked at the AAVSO data, like everyone. At first, I saw what I already saw on Twitter (see figure): it seemed like it already 2/7 pic.twitter.com/TavkOk3dP5

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Victor 🌌 @victor_astro

happened 5 times during the last 50 years. But I dug a little deeper, and I saw that in November 1985, when the luminosity was very low, a group of astronomers (Rodrigues A., Paulo) had made many measurements. ALL were very low in brightness (most around 1.8), and quite far 3/7

Victor 🌌 @victor_astro

from other astronomers’ measurements. And I thought that I had to exclude this group of astronomers from the data, but also the others which had that kind of results. So I looked at every astronomer, and I calculated their average magnitude measured. Then, I compared it to 4/7

Victor 🌌 @victor_astro

the overall magnitude average (during the same period of time). And I excluded all astronomers who had average magnitudes further than 0.3 from the overall average. I also excluded the average data points made from less than 10 data. Indeed, an average is supposed to smooth 5/7

Victor 🌌 @victor_astro

measurements errors, but if we average only 1 data, and that it is wrong, the average will also be very wrong. And I got this curve (see figure). Here, it is a lot clearer that what is happening this week has never happened in the past 50 years. It might not be a sign of an 6/7 pic.twitter.com/cHOh8n7Ghi

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Victor 🌌 @victor_astro

incoming supernova, but it remains exceptional, fascinating, as space always is. Thanks for reading me! (if I find some other interesting stuff about Betelgeuse, I’ll tweet it) @EricMamajek @NatureAstronomy @david_kipping @coreyspowell @chrislintott @JPMajor @podcastwow 7/7

Victor 🌌 @victor_astro

These are my first tweets ever, and I'm really happy that many people (and only grear people) like it, so I promise I will try to post more space stuff in the future 😄

Victor 🌌 @victor_astro

Some update on #Betelgeuse ! I was not very satisfied of the data I presented two days ago. And the reason was mainly that the optical magnitude is something quite hard to measure precisely. Indeed, normally, we measure the magnitude at a certain wavelength. The most common 1/6

Victor 🌌 @victor_astro

is the V-band. So here are the V-band magnitude data (I removed all data without uncertainty, even if I don’t display the uncertainty for clarity reasons). As we can see here, we don’t need to average anything, there a never huge divergences in the results. Also, we can see 2/6 pic.twitter.com/lTFoSEhrJY

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Victor 🌌 @victor_astro

what I showed the other day: this weeks dimming is indeed exceptional. Betelgeuse is 1.3 times dimmer than it as ever been for the past 50 years. But that’s not all. I isolated 4 past periods of impressive dimming. We can see that these dimmings are linear, and the highest 3/6 pic.twitter.com/M1Ieg4AtiV

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Victor 🌌 @victor_astro

dimming rate is of 0.0064 mag/day. Which means that every week, the #star got 4.0% less bright. But the usual rate remains around 0.0040 mag/day, which is 2.5% per week. But if we look at the last data available, we see that the current dimming rate of 4/6 pic.twitter.com/h7faqcMfGi

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Victor 🌌 @victor_astro

Betelgeuse is of 0.0100 mag/day, that’s 1.5 times faster than the fastest one I found, and it means a drop of 6.2% in luminosity every week. So, not only is Betelgeuse is fainter than ever, it’s also getting fainter at an unprecedented rate (if you find other dimming periods 5/6

Victor 🌌 @victor_astro

with a higher or comparable rate, let me know). And it hasn’t stopped, today’s data (5:58 UTC) showed a magnitude of 1.281, compared to 1.217 the 17th of December. All this is quite impressive! (even if it still doesn't mean anything about a potential #supernova) 6/6

HIROPON @hiropon_hp2

ベテルギウスについてAAVSOの過去50年分のデータを確認したところ、非常に暗いものが見つかったが、これらの報告者らのデータは暗い方に偏っていた。そこでこれらを外れ値として除外したところ、現在の暗さになったことは過去50年に1度もなかったことが明らかになった。 twitter.com/chmn_victor/st…

Con Stoitsis @vivstoitsis

Light curve for Betelgeuse. Down to mag 1.52, which is the dimmest in recorded history?. Get out and have a look pic.twitter.com/TPFX54Ug0H

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CNET News @CNETNews

Betelgeuse is acting like it's about to go supernova, even if the odds say it isn't cnet.co/3973glQ

Phil (SubStack link in bio) Plait @BadAstronomer

D O N ‘ T P A N I C Betelgeuse is *not* about to explode. It’s acting really weird, but weirdness, in this case, is only skin deep. syfy.com/syfywire/dont-…