Supernova-propelled white dwarf found zooming through Milky Way at 5 million mph | Hacker News Reader

Supernova-propelled white dwarf found zooming through Milky Way at 5 million mph

astronomy.com

104 pointsclayt681 comments

The shared link immediately redirected me to a fake malware page upon loading for the first time.

https://i.imgur.com/wOJ0b67.png

Please blacklist astronomy.com links from being shared on this site.

Also, perhaps consider shadowbanning clayt6 because judging from his account history he's apparently only here to spam astronomy.com links.

That speed (5 million mph = 2,235,200 m/s) is not quite 1% of the speed of light (299,792,458 m/s).

The article is about a large Gaia data release [1] not just the speed of one astronomical object. Maybe change the title (currently "Supernova-propelled white dwarf found zooming through Milky Way at 5 million mph ").

[1] https://www.cosmos.esa.int/web/gaia/dr2

But is it the speed of dark?

And I used to worry about asteroids..

Looking forward to the Hollywood movie in which heroes have to stop a STAR from hitting Earth.

Short of moving Earth out of the way, there's not a whole lot you can do in that case…

The mere presence of another star anywhere near earth would have catastrophic effects on the solar system.

https://www.youtube.com/watch?v=2dJEhPYfJ5U

My comment was meant as a poor attempt at humor of the impossibility of the task. You think Hollywood cares about the effects of the star's gravity? The only thing that matters is when the star collides with Earth.

There is nothing you could do with any conceivable technology. Even if a star would just traverse through the solar system it would probably throw the planets out of their orbits which would also be quite unpleasant.

Evacuation involves conceivable technology.

Conceivable, but not remotely available at the moment, or on the horizon. Not to mention, evacuation to where? The whole solar system would be thrown into disarray, and we don’t know of any Earth-like planets in other systems. We’d be toast, end of story. Maybe in a few hundred years, and given a lot of warning we could save some small fraction of humanity.

Shotgun approach: anywhere we think we might have even a remote hope of colonizing, prioritized and weighted (in terms of number of passengers) by likelihood of success.

It's amusing to think on two such populations of this human diaspora surviving to eventually reunite one day, probably tens of thousands of years after the original colonization event faded from their collective cultural memories.

Reunite? Knowing humans they'd likely battle to mutual annihilation because their toenails were different colors.

One would hope having one's solar system murdered by a rouge star might help a species grow up but right now I'm skeptical.

This was a Star Trek plot that helped explain why most of the aliens were humanoid.

https://en.wikipedia.org/wiki/The_Chase_(Star_Trek:_The_Next...

> After studying the ambiguous number blocks for hours, the discovery is made that these fragments are compatible DNA strands which have been recovered from different worlds all over the galaxy. The crew eventually believe that they have discovered an embedded genetic pattern that is constant throughout many different species, and it is speculated that this was left by an early race that pre-dates all other known civilizations. This would ultimately explain why so many races are humanoid.

Pretty sure if today's scientists had access to a dozen alien populations, DNA analysis would be one of the first things they set about. I'm not a trekky, but I would think that this should have happened chronologically much earlier in the canon.

>I'm not a trekky, but I would think that this should have happened chronologically much earlier in the canon.

Unfortunately, that was a two-part afterthought and the canon in that respect was never really explored. You could set an entire season or series around it, and Star Trek had a lot of dropped ideas with potential like that.

This is almost the plot to the Killzone franchise: as in, separate populations of human colonists at war with each other, long after they forgot their common ancestry.

That is also the plot to all of actual history. It's a pretty general plot.

Good point. Here I was thinking I stumbled onto something novel...

Well, that is not standing in the way of a good story. Interstellar solved that problem already.

Where do you want to go if planets are thrown off orbit? You need to plan that years or most likely decades before. We also have no evidence that we are capable of surviving off Earth long term.

Cixin Liu's The Dark Forest explores this idea, mostly to point out that there is no acceptable method to choose who gets evacuated and who stays behind. The author argues through his characters that any attempt at evacuation would create immediate and violent conflict between humans.

See also Seveneves[1], where a similar evacuation does indeed have some downsides. It's also a theme in one of my favorite Ted Chiang stories, "Mono no Aware"[2].

1: https://en.wikipedia.org/wiki/Seveneves

2: http://www.lightspeedmagazine.com/fiction/mono-no-aware/

Seveneves and the Dark Forest series are literally the last two (sets of) books I read and they are so wonderful. The last book in the Dark Forest series in particular has some of the most mind-blowing concepts I've encountered in SciFi.

I havent read Dark Forest but I also enjoyed Seveneves. If you want more mind blowing sci-fi I can't recommend _Diaspora_ by Greg Egan enough.

Looks great -- putting it on the list!

Violent conflict hasn't stopped things from happening in the past; it seems overwhelmingly unlikely to stop an evacuation either.

Armageddon 2: Starmageddon. Bruce Willis has to land on the surface of a star, drill down into it and release a hydrogen bomb. The fusion reaction will cause the star to blow up even though it’s already full of fusion. He’ll wear a suit made out of diamonds and have a spaceship made of diamonds, and an Aerosmith rendition of twinkle twinkle little star will play as the star explodes and diamonds rain from the sky. Now seeking story credit for this script.

Already stole the idea and have the rights secured.

All the best, - Hollywood

Codename: Brucy in the Sky of Diamonds.

But.. but diamonds are made of carbon and so can burn.

But ignorance is bliss...

The diamonds are cooled by ice water

Your script is missing how Bruce managed to escape exploding asteroid.

The explosion propelled him through the Milky Way at 5 million miles an hour until he came back around to earth.

Or how he managed to get to it. Any start exploding close enough for non-FTL technology to be a reasonable mode of transportation would also turn the Earth into dust or a molten ball of rock.

No problem... it turns out we reverse engineered a primitive FTL drive from the debris at Area 51, so we stick it onto a Space Shuttle, but it also turns out to be the only thing powerful enough to blow up the star, so it has to be detonated, sacrificing the ship.

However,the explosion also creates a wormhole that Bruce Willis bounces back into after blowing the star up, which lets him land safely back on Earth in a cool pose like Iron Man at the end.

He was propelled out of the explosion at 5 million mph.

Bruce burrowed into a floating piece of the asteroid and now has a sick man cave. Remember he is the best oil driller in the world.

spoiler alert: he dies

The film begins with government agents unearthing a refrigerator from the Nevada desert; the only known conveyance to have successfully protected a protagonist from the full brunt of a nuclear explosion.

Diamond is the best known solid conductor of heat.

Bruce would get cooked.

I'm on board with diamonds raining from the sky, tho'. Maybe on Europa. [1]

[1] https://en.wikipedia.org/wiki/2061:_Odyssey_Three

I find the idea of a stat zooming through the Milky Way to be so hilarious, but I can’t really explain why. Stars just aren’t supposed to be going on high-speed solo adventures through the galaxy in my mind. Although perhaps a better movie would be about a black hole hurtling towards earth, as they’re also supposed to be traversing the galaxy.

All stars are zooming through the Milky Way. :) The Sun does a full orbit in 225 to 250 million years. Although I have no idea why we can't calculate it more precisely than that.

My intuition is having trouble coming to grips with the notion of accelerating a fluid object to that velocity via an explosion.

It's because your intuition is on a human scales. White dwarfs apparently have a density near 1 tonne/cubic centimeter and consist of plasma which only runs analogous to fluids so far before the analogy breaks down.

One difference is that plasma will have mobile charge carriers likely imparting something similar to a London dispersion force if there's any charge directionality in the super nova blast wave. What likely has the most impact though is the density and gravity that holds the object together in a way fluid droplets on earth do not.

Since white dwarfs have around the mass of the sun in a size comparable to the Earth, the matter in them is quite exotic. Astronomer's have speculated that these hypervelocity stars (moving at a few tenths of a percent the speed of light in the referenced studies case[1]) are shot out like a slingshot. The original system is a binary, so they are already under extreme circular gravitational acceleration in their orbit. When the companion explodes in a core-collapse supernova, it loses that source of acceleration and moves in a straight line like a slingshot. The Gaia satellite is able to measure the velocity vector of the star very well, and show that it points back to an old supernova remnant. The scenario isn't controversial, but it does give quite a good example that this is how they come about.

This makes me wonder about the nature of gravity. How much of the gravitational pull from the companion would disappear? How fast? It seems like a reduction in gravity would be immediately followed by a massive energy release. It's impressive that the remaining star is moving away fast enough to avoid being destroyed in the resulting blast.

The reduction in gravity isn't due to anything special, the matter in the "anchor" star is just leaving to go somewhere else. (In all directions.)

That makes it seem like gravitationally, the anchor star would just be expanding. My intuition thinks the remaining star gets slammed by debris before the direction and strength of the anchor dissipates enough to launch it away, though my confidence in my stellar intuition is low.

Your intuition contains some truth: according to Gauss's law, the gravitation of the expanding nova shell shouldn't change at all until it passes by its surviving companion. The matter expanding away from the companion will gravitate less, but that will be canceled out by the increased attraction to the matter expanding towards the companion. Really, we're just assuming the hot, dense, and small dwarf can sustain the licking it gets when the remnant hits it. The smallness helps it get hit by less material, moreso if it's far away. It's gravitationally bound so it won't shatter - the most you could do to disassemble it would be to boil off its matter by raising it all to escape velocity. It takes a lot of energy to do that.

Right, this white dwarf is moving at ~0.8% lightspeed.

I gather that objects could be ejected from Sagittarius A* at even higher velocities.

Ahhh, this makes sense -- they're not pushed, but flung. Thank you.

That's slow on an interstellar scale for speed. A scarce fraction of the speed of light.

That's one of the fastest macroscopic solid objects with relation to its original environment.

It is an entire star traveling on hyperbolic trajectory out of Milky Way. Even at the distance where we are from the center of Milky Way the escape velocity is still over 500 km/s and if I remember the number of detected objects that are on trajectory to escape our galaxy can be counted on the fingers of your hands.

If your intuition is saying it should have gotten splashed apart: so what? The portion traveling in the same direction as the main body of the star would fall back into one body. The rest would be somewhere else, no longer a star.

a white dwarf is very much not fluid, as it's by far denser than anything you've encountered in your lifetime (or you'd had died from the gravity)

When things really get going with outer space civilizations, the idea of weaponry and conflict is going to take some surprising and horrifying turns.

We bicker about islands and aircraft carriers, nuclear arsenals and orbital ballistics, and something like this would rend the entire planet limb from limb in the blink of an eye, without breaking a sweat.

You should read The Three Body Problem trilogy for some interesting ideas in that direction.

Manipulating a white dwarf to kill a planet is like using a hydrogen bomb to kill an ant.

Imagine what that bad boy would do to perturb an entire solar system by even a near pass, though..

Given that a typical white dwarf is thought to occupy a volume comparable to the volume of earth-like planets, it strikes me as precisely the sort of object one might select to destroy a planet like earth in a single stroke.

From wikipedia:

  The estimated radii of observed white dwarfs 
  are typically between 0.8% and 2% of the 
  radius of the Sun; this is comparable to the 
  Earth's radius of approximately 0.9% solar 
  radius.

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

Catapults, naval cannons, carpet bombing cities to hit one obscure factory. War is littered with stories of absurd mismatches in economies of scale.

The problem is while it has a volume comparable to Earth, its mass is comparable to Sol! It would take an unbelievable amount of energy to move something so massive from its original position to a collision course with another body. With a fraction of that energy you could pummel a planet with a swarm of tens of thousands of giant asteroids for years.

Maybe the species in question has colonized an entire star system. This would be a good way to get rid of several nearby planets and the parent star.

I liked the story of the interstellar traders, who had a device to set off a nova, in order to ride a light sail to the next star.

The article also talks about a black hole accreting at a rate of 1% every million years that is 'currently' 20 billion solar masses.

It is 12 billion ly away, which means, if it really does continue getting 1% larger every million years it's actually ... 143,719,397,330,047,128,616,744,826,647,657,321,145,325,176,127,225,856 billion solar masses at this moment. (if the compound interest calculator is to be believed)

I really hope that's not true.

This reminds me of black hole merger recoil, in which a merger emits a gravitational wave with net linear momentum, sending the resulting black hole in the opposite direction at comparable speeds to this.

https://en.wikipedia.org/wiki/Binary_black_hole#Black-hole_m...

It’s like the machine at a batting cage that shoots the baseballs.

When they say 5 million mph, is that relative to the center of the Milky Way?

5,000,000 MPH = 8,046,720 km/h = 0.007455824656 in light speed

> ...the Gaia satellite – which precisely measured the positions, motions, colors, and luminosities of over a billion Milky Way stars ...

Can any physicists here explain how the coordinate system is constructed here?

I occasionally wonder about whether there are any objects out there traveling at a measurable fraction of c, could something even get through the atmosphere without disintegrating near those speeds?

Would something moving that quickly and carrying that much energy be more likely to disintegrate in the atmosphere, or to disintegrate the atmosphere?

Both, I suspect. At that speed, there's no point in talking about "flow" around it, it would simply compress all the atmosphere hit into a disc of plasma. The object would be disintegrated, but all the momentum has to transfer to the plasma disc instead. It would produce an impressive crater.

Relativistic baseball explores some of that.

https://what-if.xkcd.com/1/

I wish people would put high speeds in terms of miles/sec or km/s, because I know what light speed is in both, and I have a vague idea of orbital/escape speeds as well.

5,000,000 / 3,600 = 5,000 / 3.6 ~= 1,000 miles/sec.

5000 / 3.6 = 2500 / 1.8 = 1250 / 0.9 ~= 1,250 miles/sec

Could this have planets?

Well not planets, but my question is more general - could a star moving this quickly have a planetary system - obviously this one would not if it got shot out of a supernova.

Anything it passed that had a delta-v of less than the escape velocity of the white dwarf will get hoovered up.

But most of what it passed would just scatter like bowling pins.

That's 972 km/s. Escape velocity from the milky way is 537 km/s. That star is leaving the milky way.

2235.2 km/s

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