Ep. 782: Luminous Fast Blue Optical Transients

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Astronomy cast episode 782 luminous fast blue optical transits. Welcome to Astronomy

cast for weekly facts based journey through the cosmos we help you understand

not only what we know, but how we know what we know. I'm Fraser Kane. I'm the publisher

of the universe today with me as always is Dr. Pamela Gays senior scientist for the planetary

science institute and the director of Cosmic Quest. Hey Pamela, how you doing? It is we

have our first sign of spring. The snowballs, the little tiny white bulbs have come up. They

have bloomed. They haven't ruined the snow, which is what they're supposed to do. And so

we've had our first our first bulbs of spring. Yeah, we haven't had those yet. All of my

bulbs are sort of peeking through the ground now through the ground layer, but no flowers yet.

But I probably just a week or two away and flowers on my trees on my cherries. So I'm

looking forward to that. Yeah. Modern astronomy has found new ways that the universe can surprise us.

Here's one which astronomers have called luminous fast blue optical transits. They're kind of

like supernova, the kind of like gamma ray burst, but they're not like them. So what are they?

And we'll talk about a second, but it's time for break. And we're back. So I guess set the

stage when and how did astronomers sort of dawn on them? There was an entirely new class of

objects out there in the universe. And we need to also come up with an acronym or a better name

for this, but maybe we'll do that later. All right. So back in 2018, folks looking through Atlas

and Hong Kong Observatory data, followed up on a transient from the Zwicky transient facility.

So it was found in this other data set. It was backtracked to being in the Zwicky data set.

And it was catalogued. I kid you not as 80 2018 COW. The cow. The cow. Right. It's not

like a coal sign for a radio station. And I just love the fact that this stuff just serendipitously

happens because of how we name these transients. We just cycle through the alphabet over and over

and over. And it turns out the Zwicky transient facility is out there doing an obscene amount of

transient discoveries that is not getting discussed. They are able to prototype a whole lot of the

data pipelines that are going to be used for the Ruben Observatory using the Zwicky transient

facility because it is finding supernova after supernova moving object after moving object. Weirdo

blue thing in the sky after weirdo blue thing in the sky. And the cow. The cow. The cow.

It was an object that put out more light than any supernova thus far seen which was not on anyone's

bingo card. Yeah. That's impressive. Yeah. Yeah. 10 to the 44 Ergs per second. Now that's how you

describe a lot of energy. You got to stay in Ergs. It's true. It's true. And so there was a whole

lot of what on earth could cause this confusion and hopes that there would be more. Right. And the

sky did not disappoint. And for the first time in my career neither did the names. I'm going

to be stupidly excited about the names of these things because astronomers generically are

really really bad at naming things. Yes. But the next one that was found was ZTF Zwicky transient

facility. 18 ABV. The ABV is very boring. KWLA which became Koala. Right. So so this one

was also in 2018 and it was documented to reach 40,000 degrees Kelvin. They didn't have a

clear distance to it so they didn't initially have clear luminosity to it. They just knew it was

really, really hot. Right. Really hot. And since then I mean we have found probably about 10

of these objects. And and clearly some the astronomers that study this are delighted because as

you said they're giving them silly names based on a kind of a rough correlation of what the

Galbathivic alpha numeric code ends up being close to his animals. So ZTF 20 ACIG MEL. So there is a

C and there is an MEL it became the camel. Right. Then we have 2023 FHN became either the finch or

the fawn. And the most important one I think for today's discussion is AT2024 WPP. Yeah.

The wasp. Right. And this is the brightest one that has ever been seen. Yeah. Yes.

Okay. So so that's great. And so give us a sense of the characteristics of the explosion. What

makes it so much different than say a supernova or a gamma ray burst? So this is something that

for just a matter of weeks, peaks in brightness, extremely in the blue, extremely extremely

in the blue. So we're talking super hot. Right. And it's also putting out an indescribably large

amount of energy. Like this thing is is is common for you. It is the the the wasp with the most

powerful one. Put out the equivalent of take 10% of the sun's mass and just turn it into energy.

And that's how much energy it put out. Wow. Like Eagles of Square just convert that matter to

energy. Yeah. Yeah. Just straight to energy. It's not messing around. It's just like I'm here. I'm

blue. Right. I am hot. I have energy. But when we think about say gamma ray burst, right. We have

the short and long gamma ray burst where it's sort of like the two second mark. If it's less than two

seconds, that's short gamma ray burst. And those appear to be colliding neutron stars. If long,

then it's a long gamma ray burst. And those are hundreds of seconds. Yeah. And they can be yeah,

much two seconds or longer. But yeah, it can be hundreds of seconds. And that is a core collapse

supernova. Yeah. That's different from the gamma ray bursts. Yeah. These are like 20 days.

Right. And and and like why do astronomers think that they are not either gamma ray bursts or

supernova? So the gamma ray bursts, they they just don't fit with any of the gamma ray bursts

that we're seeing. They're they're not showing up in Fermi data the same way that gamma ray bursts

do. Right. If you don't look and smell like a gamma ray burst, you probably aren't a gamma ray burst.

But then the amount of energy that's coming out of them is just so much greater than what we've

seen from supernovae that initially they were like thinking maybe there's some kind of super

luminous supernovae. These are some kind of supernovae we haven't seen before. And and so people

went with that theory as one possibility. Then there was the maybe this is something that's

getting shredded, something that's getting destroyed, something that that's getting converted

from mass to energy and went down that rabbit hole as well. So so there are all these options. Yeah.

We just needed more data. Right. And and we have more data. So we're going to talk about sort of

where the scientists think we are now, but it's time for another break. And we're back.

So, you know, we did a flurry of reporting on this at university today in the last couple of months

or so where it looks like astronomers think they're starting to settle in on an explanation.

It's it's true. And and it's really cool because

again, remember you're a budding super villain, Pamela. I know. So when you say something is really

cool, other people should say, is this causing the entire destruction of a large volume of space?

Yes. Yes. I. Yeah. Yeah. The problem. Yeah. Just remember, Pamela is a super villain.

Just someone who's which is something is cool. You should be afraid.

All right. She loves super volcanoes. This is this is we're talking about here.

But yes, it is super cool. All right. So,

sometimes one answer can encompass a spectrum of behaviors. And so in this case,

it's looking like what's happening is you have stellar mass black holes for some value of stellar

mass that are consuming gas, consuming stars shredding neighbors with the wasp, the most powerful

of these thus far seen, probably being a roughly 10 solar mass black hole being orbited by a wolf

ray a star. So something young that when these two stars were on when they were zero age main

sequence stars, the one that's currently a 10 solar mass black hole was the bigger of the two

stars. The wolf ray was the smaller of the two stars. And had it been allowed to live,

they would have ended up being a binary black hole system someday. Right.

However, instead the wolf ray star got too close to the black hole, there's lots of different

things that can cause stars to migrate together. And it appears that a chunk O material was

torn off the wolf ray star as it was disrupted and that chunk of material, again, roughly 10%

of the mass of the sun, it just became energy as you do, as you do. Right. Right. So one thing

just to clarify, you said wolf ray stars are young, they are, they're in evolved form of stars,

they're yes, they're so it's a star where they've gone through the main sequence phase.

Now they've sort of blown away a lot of their outer layers, but they're, but they're massive

and yeah, and going to explode. And this is one of those times where adjectives are, are not what

we should be using. Yeah. Because a wolf ray star has an age that's still measured using

millions of civilians. Yes. And so in my brain, yeah, it never becomes old, it dies young. Yeah.

And and so, so basically they become angry teenagers and die. Yeah. Now again, super villain,

Pamela just described that event in very clinical terms. So allow me to sort of describe the

true horror of what just happened here. You've got a black hole 10 times the mass of sun

orbited by another massive, very massive star. The star got too close and the black hole tore off.

It disrupted it. A huge chunk of that star and just numbed it away, causing this extremely

bright flash. And you got this, you know, this bright blue ultraviolet flash coming from this,

this object. And it appears that these, these blue optical transits are caused when stars are

dismembered by black holes. And and there's still the potential that this could be clouds of

material getting consumed. That is not eliminated. There, there, these things come in a variety of

brightnesses. They behave slightly differently. Not all of them are going to be wolf ray stars

getting disrupted. No, which is magnificent when it does occur. But we can imagine we've lately,

there has been this amazing rash of really weird stuff getting found. So there was recently a

star found that had what appears to be two planets collided and formed a giant disc around a

settling together super Jupiter. And and we've seen before with I think was Epsilon Eriji,

where you have a binary system that has a predator planetary disc around the companion star.

So we can imagine seeing these kinds of luminous fast blue optical transients and systems where

there, there's material that hasn't formed into a star yet. What we know for certain is these

things that appear to consistently occur in galaxies with a large amount of star formation going

on in galaxies where you expect to see massive stars still living and breathing until they get

shredded by their neighbor. And and it's these kinds of systems that allow stars with ages

in the millions instead of the billions to exist where we're seeing these events occurring.

So again, it's massive stars getting disrupted, but there's the potential also for neighboring

stars to lose their planetary discs as they get eaten before life can form. And it's interesting

to sort of see like we have seen various flavors of black holes consuming stars across the universe,

but generally it's in the a supermassive black hole just tourist our apart. And the supermassive

black hole already has a Cretian disc around it. And this was a a minor addition to the overall

luminosity that is coming from the from the black hole. Or we get this situation we talked about this

I think last week or a couple of weeks ago that you can have black holes or even stars passing

through the accretian disc around a supermassive black hole and then you get that flash. But this is

much more you know that that's like a giant stepping on a bug. This is sort of a I don't know

to use the analogy like a tiger taking down something that's you know bigger than it an elephant

right. I mean the thing about this is this had the potential to be a black hole black hole system

that we would later see merge not us will be dead right someone would eventually see merge

with gravitational waves being released into a larger black hole. But this was literally a a

tensile or mass black hole saying nope you don't get to be like me you shall be my dinner.

Right and so is it doomed like there's like now it's just it's going to be meal after meal after

meal until it's gone into the accretian disc and then into the black hole and it'll never get that

chance to detonate on its own as a supernova. Exactly. Wow. Yeah. Yeah. Awesome. Again.

I mean although I think that works you know it's awesome. In that it is feel it will fill you

with all to watch it. Yes to slack job. All right we're going to talk about this some more but it's

time for another break. Do you want to make a difference in your community? Do you want to

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And we're back. So first we got to deal with one other issue here which is the name.

Yeah. It's terrible. It's terrible. I don't even remember. Hold on.

But the acronym is no better and astronomers genuinely are usually pretty good at this

so it's the terrible. It's terrible. So they named the objects well. So I asked my

audience to come up with some better names and my favorite so far is a blupernova.

What do you think? Yes. Yes please. Yes. All right so astronomers if you're listening

that is the name. They're not ellif bots. Right? They are blupernovas.

So then what does the future hold for this for the system then?

So this particular system I mean it's not possible to say with any certainty exactly how things

die. We're not there as a profession yet. But over time scales I'm not going to guess.

Yes. Shunks are going to get consumed. There will be additional luminous blue goodness

as this disrupted object forms potentially a disc as it potentially has jets. We've seen jets in

other situations. It's the case of it's dying. It has to shed its angular momentum. There's

gonna end up being a disc at some point. Discs like to build magnetic fields. Those like to build

jets. It's going to do the black holes eat things and it looks the same no matter what the scale is.

But what's cool is we're entering an age where we just started finding these less than 10 years ago.

And we're able to find it because of the zwiki transient facility. It's a fairly large scope.

It's out there just going bang, bang, bang, looking at the sky, looking for things that twinkle

flip flare move in the night. Oh I wonder if there's like another observatory. I know.

I just spoke to come online. It's gonna do that. Yeah. Southern hemisphere maybe.

So that new pipeline that is going to be able to see even more starbursts and galaxies which

are much more common in the early universe. You get that bigger mirror. You're gonna be able to

see things, resolve things further out. You're gonna be able to see more of these in its great

depths. And so I am hoping that the things that we've started to learn exist thanks to the zwiki

transient facility. We're going to get statistically significant samples of that explore the whole.

Here's the span of luminosities. Here is the span of periodicities. Here is one that's

recurring. Here is five that have jets that as we find more and more of them we're going to start

to understand all the ways that black holes eat their neighbors. And we're used to seeing this kind

of consumption and cataclysmic variables which is on our list of shows we need to do.

But we needed to do this show first because there is an object called the cow.

Right. That is excellent. Yeah. Yeah. I mean you mentioned Veer Rubin and there's actually a

couple of ultraviolet observatories that are going to be coming online. And this is a tricky one

because the wavelengths that you need to be able to detect this you need to be in space.

You need a space telescope. Yeah. And that there are a couple of ultraviolet observatories in

the works right now that should get us to this place where we can start to observe these on a

regular basis do fall in observations and cross compare with what Veer Rubin is finding.

And it's expected that we should get dozens of these every year and then you can really break

them down and say okay you know these are the ones where it's a wolf rice tarp and maybe these

are the ones where it's a regular star or a sequence star or a distinctive red dwarf or whatever

that that that you know we know that massive stars tend to come in multiple star systems.

And so then what is the trajectory of those star systems are do you get two black holes orbiting

each other which then merge you can neutron stars that merge you get a white two white dwarfs that

eventually merge do you get white dwarfs that consume off of a companion star and then you get a

type one a supernova do you get a black hole that consumes its companion or do you just get two stars

that are far away and they just never do anything mean to each other at all. So the thing that I'm

hoping that we see is we we have hints that hypernova that generate long duration

gamma ray bursts are potentially a binary system where the massive star goes supernova onto a

compact neighbor that has given it extra angular momentum. And and so we're going to be seeing

potentially systems that that compact neighbor is not just a neutron star it's a black hole.

And as you go supernova that material goes zoom and gets eaten and and and these are low

probability objects. The most massive objects are the most rare the the initial mass function of

stars is like not very many super bright ones lots and lots and lots of these really faint ones

and and then we're just left with a universe of uninteresting little tiny red stars that like

bake their baby planets. The more sample size we have the higher the likelihood we're going to

start seeing these long duration gamma ray bursts to understand what's going on and start seeing

them in more and more kinds of pairs and it's just awesome. Yep. Yep. I mean and that's the part

that I really love. I mean you know to go down into totally different rabbit hole we're sort of

moving into the same regime with exoplanets in their atmosphere. So we you know we only we know

of say 6,000 exoplanets but we only have a few dozen that their atmosphere. So we've been

imaged none that are earth sized you know around red dwarfs or around some like stars and and so we

don't know what's normal yet. We don't know what is the how these things evolve and when

new telescopes come on mind they will get these larger data and eventually we will be you know we

will know tens of thousands hundreds of thousands millions of planetary systems and we will understand

in this very rich way and then we will be able to do the same for the future of star systems that

we can look out and have enough of the universe in our minds at one time that we will understand

how things work how things play out what the future evolution looks like what the past looks like

it's a it's a very cool direction that we're heading in and a lot of these big tools

especially very Ruben are going to get us huge steps forward so any day now so we'll last

remind everybody blooper novice okay we seriously need to figure out who to write too because that

is excellent yeah but we just do you don't write to anybody you just start saying the word

until it sticks I like that all right thanks Bella thank you Fraser and thank you so much to

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Bye-bye.

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