Unknowns(Martha Hume) These odds are low but the consequences are great.Here is what we believe will happen and how to avoid it.

In the Milky Way galaxy hundreds of billions of stars are being born, which means there are hundreds of millions of these potential extermination threats we are advised to look out for. Just like stars, they move through space, but unlike stars, they emit no light, so a "stealthy" extinction could sneak up on us, unseen. The ultimate imaginable nightmare is that a black hole will collide with Earth. Even though scientists say it's unlikely, there's a lot to learn from ' What if '

Out there somewhere in the Universe, a potential doom awaits us. Although the stars in the night sky seem fixed and unmoving, much like our Sun, they’re engaged in the same gravitational dance that keeps us in orbit around the center of the Milky Way. Every stellar system out there is in motion relative to the Sun, and periodically — a few times every million years , one of these objects gets perilously close to our Solar System. When that occurs, it typically perturbs some of the members of our Oort cloud, leading to a potential barrage of comets creating light shows and showers across the planet.

Although that’s what most frequently occurs, worse outcomes can indeed befall us.for an example, Stars could pass through the Solar System, altering the orbits of the nearby planets. Other objects like neutron stars, white dwarfs, and rogue planets can do the same thing, knocking objects around like a cosmic game of pool. In the worst case scenario, you can even imagine one of these potential predators striking the Earth.

The odds of this may be unlikely but, at any moment it could happen. Astronomical timescales are very long and the Universe has many, many opportunities to create even extremely unlikely catastrophes. Here’s what will happen when an event such as this hits Earth, and what chances we will have to prevent it or do anything about it.

What are the odds of anything hitting us?

Let’s start with the good news: although we have an enormous number of potential assassins in our own galaxy, the odds that one of them will strike the Earth are incredibly small. There are an estimated 400 billion stars in the Milky Way galaxy, and even though the individual stars themselves are large, the distances between the stars are vast compared to their sizes, and the sizes of the stellar systems that they anchor.

A star our Sun, for example, is about 8699196.69 miles in diameter, and Earth orbits around our Sun at a distance of about 93205678.8 miles.(what we define as one Astronomical Unit, or A.U.): about 100 times as distant. The Kuiper belt, out beyond the orbit of Neptune, is about another 50 times as distant: several billion and billions of miles are required to map it out, and the Oort cloud persists for about a thousand times the distance to the Kuiper belt, measured in the trillions or even tens of trillions of miles.

Based on the number of stars and how they’re distributed throughout our galaxy, something we now have an extraordinary census of thanks to the achievements of the Gaia mission, we know a variety of fantastic facts about our Universe.

The stars in our neighborhood typically move at speeds relative to ,d the galactic center Almost all of the stars at our distance from the galactic center move in ellipses that are not particularly eccentric: they’re close to circles.

Almost all of them orbit in the galactic disk at our distance; very few are in the central bulge or in the larger, spheroidal galactic halo.And about half of those stars exist as part of a multi-star system, where only approximately half are like our own Solar System: with a single star all by its lonesome.

If we do the math, we can calculate, on average, how long it takes a star to get within a certain distance of our Sun. The results are interesting, but thankfully, not frightening.

Our Solar System has been around for about 4.5 billion years, or just to the left of the “10” on the x-axis on the graph above. Once every few hundred thousand years, a star comes close enough to influence our Oort cloud, with the most recent one being Scholz’s star, having done so about 70,000 years ago.


It’s unlikely, however, that any star ever came close enough to knock the other large bodies in our Solar System off course. The closest we can expect another star to have come, over our entire planet’s existence, is about ~500 A.U. away, or about ten times the distance from the Sun to Pluto. In particular, over our entire Solar System’s history, there’s only been:

a ~1% chance of a star coming close enough to disrupt our Kuiper belt,
a ~0.01% chance of a star coming close enough to disrupt Jupiter or Saturn,
and a ~0.0001% chance, or around 1-in-a-million, of a star coming close enough to gravitationally disrupt the Earth,
with only a ~0.000001% chance, or 1-in-100,000,000, of a star actually colliding with the Earth.

Given that the planets and, indeed, the Kuiper belt appear not to be disrupted from what we presume our initial configuration was some 4.5 billion years ago, these numbers pass the smell test. The greatest danger to Earth comes from a passing star disrupting our Oort cloud, and sending a potential planet-killer our way. In the far future, however, it’s almost a certainty that the gravitational dance of objects in our galaxy will lead to the eventual ejection of most planets contained within stellar systems.


Collisions aren’t the only danger

Of course,this harbinger doesn’t need to collide with you to pose a threat. If it gets close enough to you, it can: 1. gravitationally wreck your orbit,2.eject you from your stellar system entirely,3.or even spaghettify you, where the tidal forces shred the planet apart entirely.

These are things to be wary of, but fortunately, a destroyer would have to get remarkably close to cause any of these problems.

No, there isn’t any observational evidence for primordial these instruments of doom.which would be more numerous and lower in mass, and some serious theoretical difficulties stacked against their existence.

Once we understand this, we can estimate the number of threats relative to the number of stars. Approximately 0.12% of all the stars that have ever formed, or about 1-in-800 of them, are massive enough so that when they finish their life cycle, they’ll produce a stellar mass black hole: greater than about 3 solar masses but no more than a few hundred solar masses, tops. It’s plausible — although some would argue that it’s generous — that perhaps neutron star-neutron star mergers, which have been observed by gravitational wave detectors such as LIGO and Virgo, might account for up to just as many phenomenon as these massive stars do, although they’d be exclusively on the low end of the mass range.

The exterminator would have to get close enough to Earth to exert a gravitational force comparable to that of the Sun, but remember that gravity falls off as one over the distance squared. Even a black hole that was 100 times as massive as the Sun — more massive than 99% of these events in our galaxy — would have to come within about 10 Astronomical Units of the Earth to compete with the Sun in terms of a gravitational force.

That’s riskier, as there’s about a 1-in-400,000,000 chance of that happening over our Solar System’s history, but that’s only 100 times likelier than being hit by the culprit directly. (The other options, of ejection or spaghettification, fall in between those two estimates.)

Can we know it's coming?

you might think, “if a star is going to come into our Solar System and give us a serious cosmic makeover, we’ll see it coming.” But is there any way to get a warning that danger is on its way?

The answer is absolutely yes. They might not be luminous, but they do gravitate just as strongly as anything with the same amount of mass. In addition, because they aren’t extended objects that take up a large volume, like stars are, but rather are collapsed down into very small regions of space hidden behind a tiny event horizon, they strongly distort the light from objects that appear behind it relative to our perspective.

That means we have three ways to detect the presence of a black hole that gets close enough to our neighborhood.

It can cause strong gravitational lensing, where background objects that are near the same line-of-sight will have their light bent, stretched, and distorted in an easily identifiable fashion.

It can cause weak gravitational lensing, where background objects that are farther away will have their apparent shapes distorted in a way that would never occur naturally.

And it can cause microlensing, where the passing of the problem instead of occulting a background star, would amplify its light and cause a temporary but tremendous brightening; an unmistakable signature of even an invisible mass.

Is there a way to save ourselves?


In many ways, it’s clear that we’ve won the cosmic lottery by simply coming into existence, and having life survive and thrive on our planet for pretty much the entirety of its existence. What would happen, then, if we discovered we were about to lose the ultimate cosmic lottery,

Unfortunately, the only option, at that point, would be to take the Ludacris solution and get out of the way. We couldn’t move the Earth by itself; we’d have to move the entire Solar System to avoid the destruction.

The only thing that can move a Solar System by a substantial amount is, disappointingly, a gravitational interaction with another large mass. In other words, the only thing that could save us from an oncoming destroyer is the very phenomenon we’re trying to avoid: significantly gravitationally perturbing the orbits of the planets in our Solar System. If this scenario were to become reality, the only sensible course of action, after an unbroken string of billions of years of continued life on our planet, would be to either abandon spaceship Earth, or otherwise resign ourselves to going down with the ship.

I may delay abandoning Spaceship Earth until the last second but I would abandon Earth like a cowardly rat.

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