Let’s see — the Tsar Bomba nuclear weapon released the equivalent of converting about 2.3 kg of matter into energy (1).

One solar mass is about 2 x 10^30 kg, so round numbers this event released the same as 10^31 Tsar Bombas, which is … a lot of energy? That number is too big to be a good intuition pump.

Let’s try again: over the course of its entire lifetime of about 10 billion years, the sun will release about 0.034% of its mass as energy (2). So one solar mass of energy is about 3000 solar-lifetime-outputs.

So this event has released about as much energy as 45,000 suns over their entire lifetime. I’m not sure how much of the energy was released in the final few seconds of merger, but probably most of it? So… that’s a lot of energy.

(1) https://faculty.etsu.edu/gardnerr/einstein/e_mc2.htm

(2) https://solar-center.stanford.edu/FAQ/Qshrink.html

Yes! And still, gravity is so weak that that immense amount of energy translates to just a relative contraction of less than 10^-20, or about a hair's width in the distance from the Earth to the Moon.

Yes. Black hole mergers are the highest energy events in the universe in terms of watts.

I was disappointed to learn that it would require billions of solar masses of energy from a black hole merger to be able to ride the gravitational wave starting at a distance of a few Schwarzschild radii. It seems like riding a plasma jet might be better.

(Just planning my next trip.)

Into what form of energy is that mass converted?

Converted into energy and then escape the black hole, from which light can’t escape? That doesn’t seem to compute. And if it’s converted into gravity waves then we have an excellent obvious candidate for how most energy will escape a black hole. It won’t be waiting around for hawking radiation.

It's hard to wrap your head around, but that's more energy than all the stars in the observable universe combined put out during that instant

Can some of the mass escape as gas/mass flying out into space? Basically is energy the only way for mass to exit such an event?

It's like nature handed us a stress test for general relativity

Does the spinning of a spherical object cause any gravitational waves?

I believe the proposed budget is being marked up tomorrow (July 15th, 12:00). Currently the NSF budget is set to be ~$7 billion, a 23% cut compared to FY2025. I'm not sure how this affects LIGO exactly.

https://appropriations.house.gov/sites/evo-subsites/republic...

I was last week at an event in Pisa at virgo ego (basically ligo's cousin). It was to celebrate the 10th anniversary of finding gravitational waves iirc. There were an actress reading from the book the director of the Italian program wrote accompanied by the sound of waves made with sax. I can't describe it with words but it was truly moving.

There were also moments dedicated to interviewing a science communicator and the director of the virgo center, and he was, let's say, quite angry at the thought of ligo losing funding. Rightfully so

Keep an eye on whether the final FY 2026 appropriations bill keeps LIGO at two sites. Until then, it’s a real risk, but salvageable.

Given that there’s a handful of gravitational-wave observatories running globally at this point, why does the closure of one LIGO wreck triangulation?

So maybe that is why this discovery from 2023 gets published right now.

It's only spherical in a Schwarzschild (non-rotating) black hole. A rotating black hole is called a Kerr black hole, and stuff gets weird, such as there being an oblate event horizon, a weird outer horizon called an ergosphere where spacetime gets dragged along such that it's impossible to stand still and you can accelerate objects using the black hole, a weirder inner horizon called the Cauchy horizon where time travel is possible, and a singularity in the shape of a ring. Your intuition is correct that during a merger it would be weirder still.

https://en.wikipedia.org/wiki/Kerr_metric

https://arxiv.org/pdf/0706.0622

https://en.wikipedia.org/wiki/Ergosphere

https://en.wikipedia.org/wiki/Cauchy_horizon

Edit: Updated the bit about about horizons as I research a bit more. It's complicated, and I'm still not positive I have it exactly right, but I think it's now as good as I can get it.

It is difficult to talk about the shape of the event horizon because the ordinary definition of a sphere is "surface where all points are equidistant from a given point" is already complex in a differentiable manifold, but even more so when the distance is infinite because of a singularity (or the point doesn't exist/isn't unique because of geodesic structure). So you switch to a definition of "surface of constant scalar curvature with the topology of a sphere", the topology being important to distinguish it from a plane and a hyperboloid.

From there, I haven't personally done or seen the calculations of the shape of the horizon for Kerr or merging black holes, but my intuition is that it would be indeed peanut shaped for a merger (there are likely some saddle points). The coordinate shape certainly is but you can choose coordinates so that a Schwarzschild black hole is a coordinate peanut so coordinates aren't very meaningful.

Here is an animation from MIT/CalTech of what a merger looks like:

https://youtu.be/1agm33iEAuo

Does the black hole's spin deform the event horizon?

I think so?

https://archive.ph/VrzwW

Edit: "The Kerr metric also predicts the existence of an inner and outer event horizon, with the shape of these horizons being oblate rather than perfectly spherical due to the rotation."

From our perspective there is no event horizon since the collapsing star has not reached the black hole state. In fact it takes infinite amount of time from the point of view of an external observer for the event horizon to form.

In almost all situations it does matter as the collapsing star will behave as it is a black hole. But for the merge of black holes it is significant as it allows to release energy as there is no event horizon.

I'm no physicist but what I've learned on the internet through osmosis, I'd wager that black holes aren't spherical per-se, but they appear sphere-like to us dimensionally challenged beings. It's more like a manifold (mobius-gate? not a mobius surface), that changes your spatial directions to parallel temporal directions to spatial ones all leading to the singularity.

But black holes are incredibly efficient at radiating away asymmetries via gravitational waves

Is there a "mass distribution" inside? AFAIK a black hole is a singularity which means it's mass is in one (infinitely small) point.

They would merge and produce a black hole with the sum of their momentums

Because nothing can ever leave the event horizon black holes are essentially perfectly sticky.

The thing is that the spacetime around blackholes get curved to the actual extremes.

When we imagine flying "at nearly the speed of light" towards something thats traveling the same speed towards you, we tend to imagine a collision at high speeds.

But for blackholes that turn space into time and time into space, they can see the other blackhole slowing to a complete stop as its about to touch. Or it can look differently, it all depends on the position and speed of an observer.

We cant even agree on the basics like: "It doesnt matter how it looks, but they must collide", since if we look at something falling into a blackhole (which I pressume could be another blackhole just as well), we see it slow towards 0 at the edge and fade away in redshift instead of seeing it actually fall trough.

Its just all very weird and unintuitive stuff.

The escape velocity from inside the event horizon is faster than the speed of light, which is the highest possible speed in the universe.

So black holes cannot approach each other faster than the speed of light. And if their trajectories intersect perfectly, they won’t be able to escape each other’s gravity.

A black hole can’t pass “through” another black hole like two bullets hitting each other. More like two incredibly strong magnets hitting each other in midair.

Too bad we can't set up a cosmic particle accelerator to test this!

Just an amateur interested person here, but I think there is something very positive about these developments. There are probably more, that experts can chime in on, but one I know about is that gravitational waves can give us a signal of what happened when the universe came into existence. The cosmic microwave background radiation (CMB) is a similar thing with photons - it is a signal from the earliest photons to be emitted after the Big Bang / inflation. But the universe was opaque to photons for the first 300000 or so years. Even so cosmological theories have been confirmed and falsified based on this data. But gravitational waves are signals that originated right from the start, and are not blocked by anything unlike photons, and so likely give us much clearer information on the state of the universe when it was created. This might make new insights in fundamental physics possible (quantum mechanics, relativity).

This overlaps with the fascinating topic of multi-messenger astronomy: observing an event using photons, neutrinos, and now: gravitational waves, leading to triple-messenger astronomy, leading to (hand waves) more insights than.. otherwise.

How this might make real life better ln earth: that is a gamble, but progress in fundamental physics has frequently made life better on earth.

I wish you All the best in feeling better about the world.

> "how is this research going to be useful in the long run ?"

We don't know.

However, black holes are close to the limit of our scientific knowledge. We don't know what happens on the other side of an event horizon (and we may never know, at least not experimentally). Learning more about them means learning more about the universe, and every once in a while we make a breakthrough that leapfrogs our technology. There's nothing else that we can do with so much potential.

Most of the time though, the progress is quite 'boring', at least if you are not in a related field.

>practical< usefulness of this type of research isn't results per se - but methods of getting to them

LIGO needs extremely precise lasers, stationary platforms, extreme positioning precision, tons of supporting software - even if things "exist", the _need_ for results provide advances and improvements

astronomy itself already gave us cmos sensors (aka digital cameras) - but using your phone camera doesn't really make you think "this is caused by distance measurement to the stars"

Most rich civilization, to show off how great they are, have built monuments. Basically saying, look we are so rich we can redirect a big part of our society's productivity to building a magnificent piece of art. Notice, how the ancient Egyptians are remembered thousands of years later.

You should think of some research in similar ways. This is us saying, look how rich and powerful we are, we can devote a significant part of our society's productivity on discovering the very essence of this universe with no practical benefit to us. Detecting blackhole mergers is an intellectual monument.

They become a larger black hole, mostly conserving mass, minus a few percent to gravitational waves. However, their mass is proportional to their radius, not volume, so it gets LESS dense. If you laid out a bunch of black holes in a line, just barely not touching, and let them merge, suddenly, the whole sphere of space enclosing the line becomes black hole. It also turns out that a black hole with the mass of the universe would have a volume about the size of the universe.

My understanding is they just spiral into each other forever.

From our point of view nothing can actually fall into a black hole, instead it time dilates into nothing. "It is true that objects that encounter the event horizon of a black hole would appear “frozen” in time"[1]

So we would never actually see the black holes merge. In fact I'm not clear how a black hole can even form in the first place, since it would take an infinite amount of time to do so (again, from our POV).

(And yes, I know that from the POV of the falling object, they just fall in like normal. But that doesn't help us, because we'll never see it.)

[1] https://public.nrao.edu/ask/does-an-observer-see-objects-fro...

They become a more massive one. The volume of a black hole (assuming you're measuring at the event horizon) is determined only by its mass, so the final density is the same as you'd get for any other black hole of that mass regardless of how it came to be.

I don't know how to address the "consume" question. If you were pulling on a piece of fabric and two tears in it grew until they met each other to become one tear... would you say that the larger one consumed the smaller?

What happens inside cannot be known.

As I understand it, black holes are defined by three quantities: mass, spin, and charge.

I'm assuming that these quantities will be additive post-merger.

Edit: "The black holes appear to be spinning very rapidly—near the limit allowed by Einstein's theory of general relativity."

Perhaps the additive spin becomes asymptotic. Alternately, the gravitational waves might have departed with the energy of the excess spin.

My basic understanding is that they combine, basically you just add the masses together. That increased mass then means more gravity, so the event horizon is pushed further out.

We can't REALLY answer questions about what's inside the event horizon, but some real work has been done on what BH mergers look like, though even that as I understand, is extremely difficult model.

https://m.youtube.com/watch?v=5AkT4bPk-00

This is a project by ESA, it's not affected by DOGE

https://www.esa.int/Science_Exploration/Space_Science/LISA/C...

In case it's not clear, that 'chirp' is exactly what we would hear if the merger was powerful enough to actually be detectable by our ears. It's the vibration induced in the final moments and the frequency is the speed at which the blackholes are orbiting each other before they merge. Things the size of multiples of our Sun dancing around each other a thousand times per second. It's insane to me.