The Naked-Eye Sky Will (Briefly) Host a New Star

RockDoctor (Slashdot reader #15,477) wants to tell you about a "new" star that will be visible to the naked eye — without a telescope — sometime before September: By "star", I do not mean "comet", "meteorite" or "firefly", but genuine [star] photons arriving here after about 3000 years in flight, causing your eyes to see a bright point on the nighttime sky. When it happens, the star will go from needing-a- telescope-or-good-binoculars-to-see, to being the 50th (or even 30th) brightest star in the sky.

For a week or so. Of course, it could just go full-on supernova, and be visible in daylight for a few weeks, and dominate the night sky for months. But that's unlikely.
Named "T Corona Borealis" (because it's the 20th variable star studied in the constellation "Corona Borealis") it's now visible all night, all year, for about 60% of the world's population (although normally you need binoculars to see it).

But RockDoctor writes that in 2016, "T CrB" (as it is known) has started showing "a similar pattern of changes" to what happened in the late 1930s when it became one of only 10 "recurring nova" known to science: In 2023, the pattern continued and the match of details got better. The star is expected to undergo another "eruption" — becoming one of the brightest few stars in the sky, within the next couple of months. Maybe the next couple of weeks. Maybe the next couple of hours....

Last week, astrophysicist Dr Becky Smethurst posted on the expected event in her monthly "Night Sky News" video blog. If you prefer your information in text not video, the AAVSO (variable star observers) posted a news alert for it's observers a while ago. They also hosted a seminar on the star, and why it's eruption is expected Real Soon Now, which is also on YouTube. A small selection of recent papers on the subject are posted here, which also includes information on how to get the most up-to-date brightness readings (unless you're a HST / JWST / Palomar / Hawai`i / Chile telescope operator). Yes, the "big guns" of astronomy have prepared their "TOO — Target Of Opportunity" plans, and will be dropping normal observations really quickly when the news breaks and slewing TOO the target.

You won't need your eclipse glasses for this. (Dr Becky's video covers where you can send them for re-use.) But you might want to photograph the appropriate part of the sky so you'll notice when the bomb goes off. Bomb? Did I say that the best model for what is happening is a thermonuclear explosion like a H-bomb the size of the Earth detonating? Well, that's the best analogue.
This CNN article includes a nice animation from NASA illustrating the multi-star interaction that's causing the event: The stars in the orbiting pair are close enough to each other that they interact violently. The red giant becomes increasingly unstable over time as it heats up, casting off its outer layers that land as matter on the white dwarf star. The exchange of matter causes the atmosphere of the white dwarf to gradually heat until it experiences a "runaway thermonuclear reaction," resulting in a nova [according to NASA]...

The NASAUniverse account on X, formerly known as Twitter, will provide updates about the outburst and its appearance.
The BBC reiterates the key data points — that "The rare cosmic event is expected to take place sometime before September 2024. When it occurs it will likely be visible to the naked eye. No expensive telescope will be needed to witness this cosmic performance, says NASA."

Its 3000 ly away

[rossdee]

So the explosion has already happened.

Re: Its 3000 ly away

[LindleyF]

Sort of. But sort of not. Causality is weird.

Re:

[Sique]

Even more confusing: The explosions we will see in 80 years, in 160 years, in 240 years... have already happened too.

Re:

[Black Parrot]

Even more confusing: The explosions we will see in 80 years, in 160 years, in 240 years... have already happened too.

What's the deal, is it just broadcasting re-runs?

Re:Its 3000 ly away

[RockDoctor]

What's the deal, is it just broadcasting re-runs?

That is, indeed, part of the Big Question (as DrBecky considered, briefly, in her video).

These systems (large stars feeding mass onto an orbiting white dwarf are thought to be progenitors of the "type 1a supernovas" which are our most accurate "standard candles" for investigating the distant cosmos. Hence, "dark energy" - but not "dark matter" - hangs on understanding this process well.

One of the big outstanding questions in the field is whether the "metallicity" of the progenitor star meaningfully affects it's peak brightness or "rise time" (time from first-brightening to peak brightness), and decay time (fading rate of the supernova). As (possibly) the closest example of such a system, you can see the importance of observing this system as closely as possible. This is (will be) the first opportunity we've had to see one, close up, with warning, since we had detailed science on thermonuclear explosions. A lot hangs on understanding such systems as well as we can.

One of the arguments is that repeated eruptions like this cause "metals" (nuclei heavier than helium/ lithium) accumulate from one eruption to the next, until there are enough to trigger the catastrophic destruction of the entire star, instead of a (relatively - see comment about a hydrogen bomb the size of the Earth) gentle re-surfacing of the white dwarf.

Another continuing argument is over the nature of the progenitor white dwarf - is it composed primarily of carbon, nitrogen and oxygen nuclei (a "CNO" white dwarf), or is it composed of oxygen and neon nuclei (an "ONe" white dwarf, possibly with magnesium for ONeMg). Understandably, this may affect the resulting supernova, in terms of peak brightness and decay time (and possibly rise time, but for unpredicted events, that's not a huge amount of use. Probably.)

How many "re-runs" are needed to accumulate a "trigger mass" of eruption debris? Nobody knows. From the eruption history of this star, it has probably done it more than ten times previously, but at 80 years per data point, how significant that is, nobody knows.

A lot hangs on understanding these "standard candles". For example, in theory the whole paradigm of "dark energy" could be upset by understanding these eruptions, stellar systems, and the (probably) resultant supernovae better. It's unlikely to go that far, but whether the universe is 75% "dark energy", or 25% is more plausibly open for re-evaluation.

This "re-run" is probably a bigger deal then seeing "I love Lucy" yet again, even for a hungry, lust-sick alien.

Re:

[Sique]

Don't confuse Novae (as this one, a white dwarf rekindling nuclear fusion) with Ia supernovae (a neutron star imploding into a black hole).

Re:

[Barny]

When they talk of "progenitor of the type 1a supernova" they mean if, as a result of drawing in the mass of the other star, it reaches enough mass to collapse into such heavier objects as neutron stars and black holes.

It would require (IIRC) about 3.5 solar masses or so.

Re:

[RockDoctor]

The "about" there is very important. Because you're in the territory of collapsing WDs to NS (and one type of SN) or to a BH (and a different type of SN).

Which is precisely why Nature's experimental run needs watching with as much data-collection effort as can be swung in the right direction, in the first few hours.

While I think about it, what's the latest score? JD 2460429.960301, date 2024 Apr. 29.46030, magnitude 10.0391 - hasn't gone yet.

Re:

[RockDoctor]

Oh, there's also the question of whether the "eruption" ejects 99.9% of the mass accumulated, 95%, or 90%.

With a (probable ; argued, but not demonstrated) sequence of 10 eruptions for this example, the eruption probably ejects more than 90% of the accumulated mass, but that's me calculating on the back of a thumbnail, not an astrophysicist thinking it through in detail.

Re:

[habig]

It's 1.4 solar masses, the Chandrasekhar mass. The white dwarf then starts to collapse to a neutron star, but as it starts to compress the temperature shoots up past the fusion ignition point of whatever (C, O, Ne) it's made of, and *boom* runaway thermonuclear bomb. That's the type Ia SN, and recurrent novae like this are very likely how they get made.

Re:

[ceoyoyo]

A Ia supernova is a white dwarf that accretes enough material to blow itself to pieces. This one will presumably do that eventually. A type II supernova is a large star that collapses into either a neutron star or a black hole, or blows itself to smithereens, depending on its size and metallicity.

Re:

[RockDoctor]

This one will presumably do that eventually.

Welll ... It is quite sensitive to the mass. And to the metallicity.

Which uncertainties are precisely Why this "close", "well-understood" example is important. If (unlikely) it goes exactly per Group1's expectations. then Group2 will disagree, strenuously.

If (unlikely) the "bang" happens on 2024-05-01.00001, then the disputes will start at. approximately. 2024-05-01.0002.

And, as normal - has it "gone"? JD 2460430.385620 date 2024 Apr. 29.88562 mag 7.118.

OK, ha

Re:

[RockDoctor]

The database has added another entry, timed between the previous ones. And valued similarly.

JD 2460430.385620, Date 2024 Apr. 29.88562 mag 7.118

JD 2460430.385389, Date 2024 Apr. 29.88539 mag 8.835

JD 2460430.385046, Date 2024 Apr. 29.88505 mag 11.250

That looks like it has "gone". And I'm going to STOP interrogating the database, because the "big boys" need that access. And that is precisely why I didn't post a direct link into the database. The "Slashdot Effect" may be history, but now is not the time

Re:

[RockDoctor]

Still only that one observer who has reported low (bright) magnitudes. Other observers aren't reporting a significant change.

Re:

[Sique]

In some way, yes. It's a periodic process where T Corona Borealis pulls gas from a nearby star until there is enough to restart nuclear fusion, then it burns for some month through the gas and stops again. This is different from an Ia supernova, during which a neutron star captures enough gas from a nearby star to collapse into a black hole.

Re:

[RockDoctor]

This is different from an Ia supernova, during which a neutron star captures enough gas from a nearby star to collapse into a black hole.

That depends on the nature of the underlying white dwarf - it is hypothesised. A CNO (Carbon- Nitrogen- Oxygen) white dwarf is thought to disrupt completely by everything fusing in seconds. A ONe(Mg) (Oxygen- Neon- [maybe Magnesium]) white dwarf on the other hand is thought to disappear down the plug hole of forming a neutron star then (possibly) a black dwarf.

Which is th

Re:

[RockDoctor]

Always of course hoping that the later ones in the pipeline include a supernova. We need that baseline data with modern instrumentation. What we have from 1946 is a lot of visual magnitude estimates, and a handful of spectra of very limited resolution.

Re:Its 3000 ly away

[ControlFreal]

Yes, and no. Yes, if you work off the model where there is a universal "now", and light just happens to travel at some high speed. In that model, the explosion happened, and we are now just waiting for the light to finally arrive. However, the problem with that model is that there is no universal "now".

So no: The speed of light is not related to light. Light travels at that speed, but there is nothing about the properties of light that somehow determines that speed; other things, such as gravitational interactions, travel at that speed as well. That speed is not just some arbitrary speed limit, but rather the speed of causality, full stop. There is nothing at point A that can even influence point B in less time. This is what determines our past light cone, or rather, our past causality cone.

And to be clear: this star's bright light-up is not in our past light cone, and so, for us, it did not yet happen.

Re:

[RockDoctor]

However, the problem with that model is that there is no universal "now".

As Einstein pointed out with his demolition of the concept of simultaneity in his 1905 paper on ... it was the "Electrodynamics" one, wasn't it? Been a while since I read them.

If SR is true (and it agrees with experiment to high precision, until you get into the realm of GR), then there is, indeed, no "now" except for "here".

Re:

[Sique]

The problem being that SR exists in a realm called Spacetime. Thus just the time coordinate is not sufficient to describe an event, you always need the space coordinates too, and vice versa, just the space coordinats are not sufficient, you need the time component.

Re:Its 3000 ly away

[i.r.id10t]

According to the First Scroll of Wen the Eternally Surprised, Wen stepped out of the cave where he had received enlightenment and into the dawning light of the first day of the rest of his life. He stared at the rising sun for some time, because he had never seen it before. He prodded with a sandal the dozing form of Clodpool the apprentice, and said: 'I have seen. Now I understand.' Then he stopped, and looked at the thing next to Clodpool. 'What is that amazing thing?' he said. 'Er ... er ... it's a tree, master,' said Clodpool, still not quite awake. 'Remember? It was there yesterday.' 'There was no yesterday.' 'Er ... er ... I think there was, master,' said Clodpool, struggling to his feet. 'Remember? We came up here and I cooked a meal, and had the rind off your sklang because you didn't want it.' 'I remember yesterday,' said Wen thoughtfully. 'But the memory is in my head now. Was yesterday real? Or is it only the memory that is real? Truly, yesterday I was not born.' Clodpool's face became a mask of agonized incomprehension. 'Dear stupid Clodpool, I have learned everything,' said Wen. 'In the cup of the hand there is no past, no future. There is only now. There is no time but the present. We have a great deal to do.' Clodpool hesitated. There was something new about his master. There was a glow in his eyes and, when he moved, there were strange silvery-blue lights in the air, like reflections from liquid mirrors. 'She has told me everything,' Wen went on. 'I know that time was made for men, not the other way round. I have learned how to shape it and bend it. I know how to make a moment last for ever, because it already has. And I can teach these skills even to you, Clodpool. I have heard the heartbeat of the universe. I know the answers to many questions. Ask me.' The apprentice gave him a bleary look. It was too early in the morning for it to be early in the morning. That was the only thing that he currently knew for sure. 'Er ... what does master want for breakfast?' he said. Wen looked down from their camp and across the snowfields and purple mountains to the golden daylight creating the world, and mused upon certain aspects of humanity. 'Ah,' he said. 'One of the difficult ones.'

Terry Pratchett, Thief of Time

Re:

[ceoyoyo]

That depends on how fast you're moving, and in what direction.

Or, the sensible interpretation, everything has already happened.

Brightness

[4im]

To put this into perspective - it's supposed to reach the brightness of the north star Polaris. If you're somewhat familiar with the sky, that's actually not *that* bright.Visible, sure, but not necessarily if you're in a much light polluted area.

I can only hope the effing cloud cover is going to finally break a bit in my area, it's been about half a year since I had any opportunity to do anything deep sky.

Re:

[RockDoctor]

that's actually not *that* bright.

As I said in my original submission (and EditorDavid waved the blue pencil over),

the 50th (or even 30th) brightest star in the sky

.

Making the (optimistic?) assumption that the average Slashdot user can count to 11 without removing pants or socks, that means that the affected "quadrant" (one quarter of the above-horizon sky) would go from having 4-to-6 stars this bright to having 5-to-7 stars this bright. Not going to knock your socks off, but should be visible to anyone wh

Degenerate matter is neat

[Rei]

White dwarfs are composed of electron-degenerate matter. With most matter, volume changes with temperature. This is a natural check on nuclear reaction rates - as they increase, they heat up their environment, causing it to expand, reduce density, and slow the reaction. But degenerate matter's volume is almost independent of its temperature, so it lacks this natural counterbalance; degeneracy pressure is what keeps its volume, not thermal pressure. As a result it tends to be kind of... explodey ;) You have to get the temperature so high that thermal pressure becomes relevant again for it to meaningfully expand.

A deepness in the sky!

[DarkLordBelial]

Our very own OnOff.

T Coronae Borealis, dammit!

[Applehu Akbar]

Whatever happened to using the Latin genitive when identifying objects in a constellation? The brightest star in Gemini, for example, would be Alpha Geminorum.

Re:

[RockDoctor]

And how does that work with noun-phrases, rather than single-word nouns?

Actually, Wiki covers this. The constellation is Corona Borealis, it's genitive is, indeed Coronae Borealis.

I may have been sloppy in my typing - I know of the convention, but never having formally studied Latin, it doesn't appear in my internal spell-checker.

Now, which Duolingo course to do this evening - Swahili, French (revision), German, Spanish (learning beyond my schooling), or Russian? Oh, I forgot Portuguese - but that's so s

Re:

[cusco]

A friend knew French and Spanish, and tried to learn Portuguese. Confused her completely, and for a week or so she couldn't communicate in any of the three.

Re:

[RockDoctor]

I found that I could understand enough of written Portuguese to get by, and if I didn't have a particular bit of Portuguese vocabulary, then the corresponding bit of Spanish would generally be understood.

But yeah, the Arabic influence in Portuguese is a lot stronger than in Spanish, and there are a lot of differences. I can see getting hung up on that.

not a nice animation

[at10u8]

That animation is an abomination. I cannot say what it depicts, but it is not T CrB. I cannot explain the physics that animation does depict. Before I was born Bob Kraft explained how T CrB works, and it is not like that animation.
https://ui.adsabs.harvard.edu/... [harvard.edu]

Re:

[RockDoctor]

Yeah, it's not a very good animation. I think the latter part of the animation is trying to express the long (year and a bit) post-eruption "high" brightness state seen in the 1946 eruption as some effect of irradiation of the primary by the secondary, but it's not very clear.

Before I was born Bob Kraft explained how T CrB works, and it is not like that animation.

I think ideas have got considerably more detailed than that, with another half-century of work. But yes, the basic idea of accumulating mass onto

Not "Visible all night, all year"...

[Jerrry]

From the /. story:

it's now visible all night, all year, for about 60% of the world's population

Sorry, but at a declination of 25 degrees, 55' north, T Coronae Borealis is not visible all night, all year in the northern hemisphere. It's only circumpolar at latitudes north of about 64 degrees. Everywhere else it rises and sets like all other objects in the sky.

Re:

[RockDoctor]

And in the blue corner, dribbling to himself, is the "electric universe" dude.

Harmless, but noisy and distracting. Like flatulence.

Are we hot?

[RockDoctor]

JD 2460430.385620, date 2024 Apr. 29.88562 mag 7.118

JD 2460430.385389, date 2024 Apr. 29.88539 mag 8.835

JD 2460430.385046, date 2024 Apr. 29.88505 mag 11.250

JD 2460430.384698, date 2024 Apr. 29.88470 mag 9.890

Reporting magnitudes above 8.0 has been explicitly discouraged unless you're really sure.

Either someone (observatory code not given above) is going to be very embarrassed, or a lot of BIG telescopes are dropping their metaphorical cookies and slewing to "TOO".

Am I over-cooking one datum? Good quest

Re:

[RockDoctor]

Ahhh - fuck. Reports come from ONE observatory. So could be local decrease in cloud cover. Booo!

Re:

[RockDoctor]

There is a string of a half-dozen reports in the last couple of hours at (about) 7.5 mag.

Plateauing. .. ?

Apostraphe Police

[HaydonBerrow]

"AAVSO (variable star observers) posted a news alert for it's observers a while ago"

Re:

[RockDoctor]

Yes. And it's a public report. So? It's jargon-y, but perfectly comprehensible.