Gaia's first black hole discovery: GAIA-BH1 (2022)
cosmos.esa.int
cosmos.esa.int
Given this and the difficulty in spotting dormant black holes, it will be interesting to see if these black holes are suprisingly common. Similar to the way gravitational microlensing led astronomers to find far more low-mass planets than they expected.
We know BHs should be pretty common. Earlier generations of stars were composed of larger and more short lived stars (due to their low metallicity) that should mostly end up as black holes.
As to detecting gravitational microlensing it is not as easy as it sounds. A black hole remnant of a star will be microlensing the light just like a star -- only without very visible reason for the microlensing to be happening.
In practice what you would see is when a black hole moves in front of a star that star's light is suddenly magnified without any good reason. It is one time event, it is rare and afterwards there is nothing else to study. These types of events tend to be very hard to capture because they require you to look at entire sky all the time.
As a matter of fact, many ancient civilizations have “Gods” for the point where moon’s orbit intersects with Earth. https://en.wikipedia.org/wiki/Lunar_node
In Hindu mythology - we have two “shadow planets” and gods called Rahu and Ketu https://en.wikipedia.org/wiki/Rahu these points are no real planets or moons - but are given the same status.
Anyone here who's familiar with black hole formation and who could elaborate on why the BH is so special?
Formation of a black hole is a pretty violent event - a supernova. Which sometimes ejects a companion star, and would certainly strip it of mass and change its chemical composition.
(edit) One other thing that makes a black hole 'special' is if they're really light (possibly formed via two neutron stars colliding).
> The fact that the star is very similar to the Sun is also quite special. It is different from the companions of most other known black holes (see the location of the newly found Gaia-BH1 with respect to the other known black holes as highlighted in Figure 1). If this system also contains planets, like a large fraction of solar-type stars do, it would be an even more interesting object for further studies!
https://en.wikipedia.org/wiki/Black_hole#Formation_and_evolu...
> The distance between star and companion is about the same as the average Earth-Sun distance
So quite close.
Maybe something interesting is in these links:
https://en.wikipedia.org/wiki/Astronomical_naming_convention...
Really super terrified, right?
Moreover, black holes aren't death machines or anything. This black hole puts out much less light and energy than an equivalent-mass star. It's quite safe.
If the Sun were replaced with a black hole of equal mass, apart from the heat and light going out, we wouldn't notice anything. All the planets would still orbit more-or-less the same.
Famous last words...
To fall into the former Sun black hole would be much more difficult than falling into the Sun as it is now. You'd pretty much have to make a deliberate effort to "land" on the event horizon.
Black holes are just massive objects, no different from any other "massive object" in the universe. It's pretty easy / common for stuff to orbit massive objects, rather than fall into them. Furthermore I vaguely remember her mentioning another force involved with pushing things away from black holes, such that physicists of today aren't able to reach consensus on the idea that maybe one day all mass in the universe will be in one black hole or another, it seems there's other forces involved that may prevent that from happening (though there are hypothesis around that time is a cycle of all things falling into a universal singularity which then explodes into a big bag and the cycle continues).
In short though, no, you shouldn't be terrified. There has been an ongoing theory for a while that there's a micro black hole somewhere near pluto causing our predictions for its orbit to be just ever so slightly off. https://www.newscientist.com/article/mg24933280-100-is-there... If it's there, it's been there basically forever, and its event horizon, if it's a micro black hole, is hilariously small.
https://www.goodreads.com/en/book/show/61324554
Also as others have said, if it's coming directly for earth, it would take at least 1500 years to get here, which is plenty of time for humans to do something about it. Almost certainly you'll already be dead anyway.
There are a couple of comically improbable conditions that would happen only in fantasy to start threating us
The same, of course, could be said for any other celestial body, currently observed or otherwise.
But why bother with this black hole? If you want to go that route, why not just imagine that there could be a 100-solar-mass something headed directly at us at 0.9 c, and it will show up tomorrow?
Right, good point! I shouldn't have skipped my morning coffee.
> if it was hit by something big
For the record, I assume you mean not a literal "hit" but some sort of binary interaction with another very massive object that ends up transferring (a lot of) momentum to the black hole.
The reason we wouldn't be able to know until it's too late is due to the nature of light and the speed at which information can travel.
When we observe celestial objects like stars or black holes, we do so by detecting the light they emit or the effects they have on nearby objects. The speed of light is approximately 299,792 kilometers per second (km/s) in a vacuum. This speed is the fastest anything can travel, including information.
In the hypothetical scenario presented in the comments, if a black hole or any celestial body was approaching Earth at near the speed of light, the light (or information) about its approach would be traveling towards us at almost the same speed as the object itself. This means that by the time we receive and process the information about its approach, the object would already be dangerously close to us.
In simpler terms, imagine you and a friend are racing towards a finish line, and your friend is just slightly slower than you. If you start the race at the same time, you'll reach the finish line almost simultaneously. In this analogy, you represent the light (information) and your friend represents the celestial object. Since the information about the approaching object is only slightly ahead of the object itself, we wouldn't have much time to react or prepare once we become aware of the threat.
In the case of the black hole discussed in the comments, if it were moving towards us at near the speed of light, we wouldn't know it until it was almost upon us, making it too late to effectively respond or take any meaningful action to protect ourselves.
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Human comment: Near light speeds are a fascinating topic, that even though I claim basic understanding it always defies intuition.
This is pure clickbait.
(Diaspora is a much more appealing story, at least for me, and probably my fave of his novels, but Incandescence does something unique: a discovery fiction of people figuring out elements of general relativity before newtonian mechanics.)