New type of Supernova explains ancient mystery | Hacker News Reader

New type of Supernova explains ancient mystery

bigthink.com

30 pointsStartupSven14 comments

> This supernova, about 31 million light-years from Earth in the galaxy NGC2146, was detected three hours after the explosion happened.

Faster Than Light communication!

That confused me, too. It seems to refer to this from the paper:

    On 2018 March 2.49 (UT dates are used throughout), we dis-covered AT 2018zd13 at an unfiltered optical magnitude of 17.8 in the outskirts of NGC 2146... Combined with our pre-discovery detection at 18.1 mag on 2018 March 1.54, we estimate an explosion epoch of 2018 March 1.4 ± 0.1 (~3 h before the first detection;

I'm not entirely sure I understand the date/time format, but the last part suggests that TFA meant "We pointed our telescope at it when the explosion was already in progress. We think it had been going for about three hours at that point."

I think "March 2.49" means ".49 of the way through March 2", so 11:46 AM, but that's just a guess. I've never seen that before. If so, that "first detection" was at 12:58PM on March 1, and they figure it actually started at 9:36AM... about three hours earlier.

That's the first thing that stood out to me as well, but it's actually pretty accurate when it comes to light speed communication. It was basically 3 hours after the event observable by us, which is for all practical purposes "when it happened". There is no true universal "when it happened", it's all relative.

Technically light doesn't experience time.

Which means there's no such thing as "how much time it takes light to travel from the Sun to Earth". It takes no time at all. Yet we do say "8 minutes 20 seconds". Everyone would claim that's the correct answer. In which case at the point of detecting this light on Earth, if someone asks us "when did the event of it leaving the Sun occur" you'd obviously say "8 minutes 20 seconds ago".

So while there's no true universal "when it happened", we're all here on Earth and we've developed a certain way of expressing ourselves about time and light, and broadly speaking we're all sharing a relative point of view in spacetime, relative to something 31 million light years away.

So to say "we detected it 3 hours after it happened" when it happened 31 million lights away would be poorly written, simply put.

There is only one event that happened, the question is how much time we will measure between that moment and the photons of the event reaching earth.

In the reference frame of earth it is 31 mio years. In frames that move faster and faster to the speed of light, relative to ours, this would take less and less time, an effect known as time dilation.

Obviously the article means that 3 hours after the first photons of this event reached earth (and we see it as happened), we managed to aim our sensors towards it and start measuring. It looks a bit clumsy indeed.

Another way to think about it would to change the distance and see if the sentence still makes sense. If the event was on the other side of the world, 100 light-milliseconds away, it wouldn't be an issue. If it happened on Mars, a light-minute or so away, also not an issue. If it happened on the Sun, 8 light-minutes away, this phrasing would also be fine, same for Jupiter and even Pluto. Not sure where the line is, but it's somewhere between 10 light-minutes and 31 million light-years, I guess :P

I don't follow the connection with the Crab Nebula supernova. They claim that the supernova was this type III, but what about it leads to that claim? The article states it without support.

It is believed Crab Nebula is the remnant of the 1054 supernova. We have detailed drawings of where in the sky it occured, and the Crab Nebula lies in a consistent location.

Right, I understand that, but what I don't understand is, what points to that supernova being a type III supernova?

Hmm, haven’t read the article in enough detail, but again, the observations at the time, meticulously and redundantly kept, do not square up with what we see in the Crab Nebula. The original supernova light profile (eg how long it was visible in daylight for) doesn’t match what’s left for other known supernova types. Their light profiles are very specific to the type of explosion.

This has been an open issue for a while.

Gotcha, thanks :-)

Can someone explain? - if neutral atomic nuclei with internal electrons can exist, why are they not visible in particle accelarators? - what atoms are we talking about? Atoms too heavy to gain energy by fusing? Thanks

A particle accelerator smashes streams of particles head on, but can it simulate properly the internal structure of a star before supernova where unbelievable forces are occurring in 3 dimensions in relative stability?

I'd think to simulate you basically need to prevent the electrons from going anywhere, and the only place to go is inside the nucleus, where the strict rules of quantum mechanics and particle physics dictate they get merged with protons to form neutrons.

Do we have anything besides tokamaks for smushing things together? Tokamaks seem to peak out at low-energy fusion reactions, but all I read about tokamaks is engineering focused on net-positive fusion.

Electron capture indicates conversion of protons and electrons to neutrons and electron neutrinos.

The core of a star is already very hot and further collapse raises the temperature, so we’re probably talking about photodisintegration of any heavy nuclei into alpha particles, as electron capture process runs.

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