A Star Is About to Explode (And You'll Be Able to See It)

T Corona Borealis, a star in the constellation Corona Borealis, undergoes periodic explosive brightness variations every 80 years due to a binary system involving a red giant and a white dwarf. As the red giant expands, gas transfers to the white dwarf, leading to thermonuclear fusion on its surface and resulting in a nova. This phenomenon has been observed for centuries, evidenced by gas shells from previous explosions. Although not extraordinarily bright, T Corona Borealis is significant due to its relative proximity and the opportunity it presents for detailed study with modern telescopes.

• T Corona Borealis is a star located in the constellation Corona Borealis, which translates to "Northern Crown" from Latin.
• The system is approximately 2,600 light years away from Earth, meaning any observation we make today reflects events that occurred 2,600 years ago.
• T Corona Borealis is a variable star, meaning its brightness changes significantly and explosively over time.

“In the northern hemisphere, we have Corona Borealis and one of the stars in that constellation varies in brightness significantly explosively.”

• This star is the third discovered variable star in the constellation, identified by the letter T following the convention of starting with R.

“The way we identify variable stars in a constellation is we start lettering them from R, so this is T Corona Borealis.”

• The phenomenon where a star's luminosity explosively varies is known as a "Nova," derived from the Latin word for "new."

“If you didn't know it was in the sky and then it exploded, you would say, 'Oh, there's a new star in the sky.' What's Latin for new? Nova.”

• T Corona Borealis is part of a binary star system consisting of a red giant and a white dwarf.
• The white dwarf is a dead star that glows from residual heat, and our Sun is expected to become a white dwarf in about 5 billion years.

“There's a red giant and a white dwarf, and the white dwarf is dead. It's glowing from leftover heat from when it was an authentic star.”

• The Sun will shed its outer layers and reveal a dense core about the size of Earth, which will cool over eons.

“The Sun will die as a white dwarf when the Sun in 5 billion years sheds all of its outer layers. It will reveal a dense core, about the size of the Earth, that will be a white dwarf.”

• In this binary system, the red giant continues to expand and become more bulbous over time.

“This white dwarf is in a binary orbiting system with the red giant, and red giants like becoming bulbous, and they keep expanding and expanding.”

These notes provide a comprehensive overview of the key ideas and topics discussed in the transcript, offering detailed insights into T Corona Borealis, its characteristics, and the dynamics within its binary star system.

• There is a specific balance point between two celestial objects where expanding gas, if it crosses this point, is no longer gravitationally bound to the red giant and will fall into the white dwarf.
• This balance point is crucial for the transfer of gas from the red giant to the white dwarf.

"Here's a balance point, a literal balance point, between these two objects where if the expanding gas crosses that balance point, it's a gravitational balance point. Then it's no longer gravitationally bound to the red giant and it will fall into the white dwarf."

• The balance point determines whether the gas will remain with the red giant or transfer to the white dwarf.

• As the red giant expands, it reaches a point where it fills a region of space known as the Roche lobe.
• The gas from the red giant crosses this lobe and lands on the white dwarf.

"There's a gas transfer, and this transfer point as the red giant gets larger and larger, there's what we call a lobe, an envelope of space around it, and it was first described mathematically by a fellow named Roche. So it fills his Roche lobe, and the gas crosses over and lands gently on the white dwarf."

• The Roche lobe is a critical concept in the transfer of gas between binary star systems.

• Hydrogen accumulates on the surface of the white dwarf as the gas transfer continues.
• The pressure and temperature at the base of this hydrogen layer increase due to the solid nature of the white dwarf.

"So now we have hydrogen on the surface of a white dwarf and this continues and it accumulates. As that continues, the pressure builds because the white dwarf is basically solid matter, and you have gas falling on it. At the base of the gas, the pressure is growing and the temperature is growing."

• The accumulation of hydrogen and the increasing pressure and temperature are precursors to a significant astronomical event.

• The situation becomes unstable as the pressure on the hydrogen layer increases, leading to spontaneous thermonuclear fusion.
• Unlike the Sun, which contains fusion in its core, the fusion on the surface of the white dwarf causes a catastrophic explosion, visible as a Nova.

"Eventually, there's enough gas pressure down on that hydrogen layer that it ignites spontaneous thermonuclear fusion. The Sun is doing that in its core every second of every day, but if you did that on your surface, you will blow out all of the gas that was there catastrophically because it is uncontained. This is what is visibly a Nova seen in the night sky."

• The uncontained nature of surface fusion on the white dwarf leads to a Nova, a dramatic and observable event in the night sky.

• T Corona Borealis has been observed to repeat this Nova event approximately every 80 years.
• Historical evidence and deep photos from specialized telescopes show shells of gas moving away from the system, recording past explosions.

"T Corona Borealis has been repeating this every 80 years. We have evidence of this going back centuries. Every time it explodes, there's a gas layer moving slowly away from the system. We have deep photos from specialized telescopes that reveal these shells of gas, offering a record of all the."

• The recurrence of Nova in T Corona Borealis and the evidence from gas shells provide valuable insights into the behavior of this binary star system.

• A Nova is a phenomenon where a star suddenly increases in brightness and then slowly fades back to its original state.
• The specific Nova discussed here has recently reached a brightness magnitude of 2.5.
• Magnitude 2.5 is comparable to the brightness of the North Star, which is not as bright as commonly perceived.

"The brightness reaches about magnitude two and a half and that's astronomer lingo for about the brightness of the North Star."

• Magnitude 2.5 is a technical term in astronomy indicating a certain level of brightness.

"Many people think the North Star is bright and distinct in the night sky but it's not. It's just not like get over it. The North Star is not in the top 10. It's not even in the top 40. The North Star is the 49th brightest star in the night sky."

• The North Star is often mistakenly believed to be one of the brightest stars, but it is actually the 49th brightest.

• The recent Nova will be one of the best-studied due to the availability of modern telescopes, including space telescopes.
• Historically, there were fewer telescopes, limiting the study of such events.

"So this will be the best studied Nova there ever was simply because of its timing and its brightness."

• The timing and brightness of this Nova, combined with current technology, will make it the most thoroughly studied Nova to date.

"The last time it blew we didn't have that many telescopes in the world and certainly weren't space telescopes."

• The previous occurrence of this Nova had limited observational capabilities compared to today.

• Around 50 Novae are discovered each year, some of which are repeating events.
• T Coronae Borealis (T CrB) is one of the brightest repeating Novae due to its proximity to Earth.

"Even though there's 50 or so Novi discovered each year some of them are repeating, this one T Coronae Borealis is one of the brightest simply because of how close it is to us relative to the others."

• T CrB's brightness is attributed to its relative closeness to Earth compared to other Novae.

• Novae recur due to a cyclical process involving a red giant star and its Roche lobe.
• The red giant spills hydrogen and some helium into the Roche lobe until it reaches a threshold, causing an explosion.

"Once you have the explosion we start the cycle all over again. The red giant spills out of its Roche lobe and layers hydrogen gas and some helium until it hits that threshold once again."

• The cyclical nature of Novae involves the accumulation of gases until an explosive threshold is reached.

• This specific Nova recurs approximately every 80 years, making it a rare event within a human lifetime.
• Comparisons are made to the perception of eclipses being once-in-a-lifetime events, which is often exaggerated.

"The fact that this repeats every 80 years means yeah that's a once in a-lifetime event. We've all heard people describe eclipses that way once in a lifetime event well that's just BS."

• The 80-year recurrence makes this Nova a notable but not unique event within a human lifespan, similar to how eclipses are often mischaracterized as once-in-a-lifetime.

• Solar eclipses occur somewhere in the world approximately every 2.5 years.
• They are more frequent on Earth than the Olympics.

"There's an eclipse, a total solar eclipse somewhere in the world every 2 and a half years or they're simply not coming to you that often but they're coming to Earth more often than the Olympics."

• Eclipses are frequent global phenomena but may not be visible from any single location as often.

• Binary systems consist of two stars, often with different stages of evolution such as a red giant and a white dwarf.
• The interaction between these stars can lead to significant astronomical events.

"There's another kind of object out there where you have a binary system once again a red giant and a white dwarf."

• Binary star systems can lead to phenomena like novas and supernovas due to mass transfer between the stars.

• The Chandrasekhar Limit is a critical mass threshold for white dwarfs, approximately 1.4 times the mass of the Sun.
• Beyond this limit, further mass accumulation causes the white dwarf to become unstable and collapse into a supernova.

"If the white dwarf is already near a different kind of threshold in Mass, a threshold first calculated by the brilliant Indian astrophysicist Subrahmanyan Chandrasekhar."

• The Chandrasekhar Limit is fundamental in understanding the transition from white dwarf to supernova.

• Novas and supernovas are both explosive events in binary systems but differ significantly in intensity and outcome.
• A nova involves the explosion of the outer surface of a white dwarf, while a supernova involves the complete collapse and explosion of the white dwarf.

"If you have a white dwarf that's near a limit...and you drop some more material on it...the entire star white dwarf goes unstable and it collapses and becomes a supernova."

• Supernovas are immensely brighter and more catastrophic compared to novas.

"These are way brighter than novi...one is way brighter than the other because one is the catastrophic death of the white dwarf and the other one is just sort of puffing off."

• The brightness of a supernova can be seen halfway across the universe, comparable to the brightness of an entire galaxy.

"Supernova you can see halfway across the universe that's how bright they are they're as bright as the entire galaxy in which they explode."

• The discussed nova, t Corona Borealis, is at a safe distance of 2600 light years from Earth.
• There is no immediate threat to life on Earth from this nova.

"This Nova we are at a safe distance 2600 light years uh you can sleep well at night knowing life on Earth will not end from that."

• Understanding the distances and scales of these events helps contextualize their impact on Earth.

[Music]

• The transcript ends with a musical interlude, indicating the conclusion of the discussion.