About That Monstrous Black Hole We're All Orbiting (theatlantic.com)

Astronomers on Wednesday reported new telescope observations of the environment around the Milky Way's supermassive black hole, named Sagittarius A*, pronounced "a-star," and they transformed the data into a lively animation. From a report: The video is positively ghostly. Clumps of gas swirl around the black hole, traveling at about 30 percent of the speed of light. Astronomers collected the data for the visualization using an instrument on the European Southern Observatory's Very Large Telescope, located in the deserts of northern Chile. The instrument, appropriately named GRAVITY, detected flares of infrared radiation coming from the disk surrounding Sagittarius A*. The researchers believe the bursts originated very close to the black hole, in an incredibly tumultuous region known as the innermost stable orbit. Here, cosmic material is slung around violently, but it remains far away enough that it can circle the black hole safely without getting sucked into the darkness.

If the thought of orbiting a monstrous, star-gobbling black hole spooks you, don't worry. Earth, located about two-thirds out from the center of the Milky Way, is at a very safe distance. The planet is in no danger of being consumed and wiped off the face of the universe. But, like everything else in the galaxy, it has long been subject to the black hole's whims. When black holes belch radiation out into space, the outflow can heat surrounding gas so much that it prevents it from cooling. If cosmic dust can't cool, it can't condense to form individual, brand-new stars, including ones like our sun. Scientists suspect that the fates of galaxies -- whether they produce new stars or stop altogether -- rests with the supermassive black holes at their centers.

Comments

Re:We're all going to dieeeeee!!!!

[Rei]

Even before the sun's red giant phase it will have doubled in luminosity. Assuming no feedback effects, that would increase Earth's equilibrium temperature by 19% on an absolute temperature scale. So if you assume that feedback mechanisms remain the same, you're talking at least 50 degrees celsius temperature increase.

Of course, that's far too simplistic of an approach to take; feedback levels will change, and the details of that are a complex modeling task. Runaway greenhouse effects are quite possible (such as: loss of crustal water = reduce crustal viscosity = reduced / eliminated large-scale plate tectonics = Venus-like geology).

Of course, the biggest question is whether any sort of sentient life would exist in the system at that point in time. If so, it would likely be so far advanced (billions of years of technological development) that building an orbital solar reflector would be a laughably trivial task, and even relocating the planet might be within their reach. The ultimate achievement would be if they were to develop technology to siphon off matter from the sun over billions of years, ultimately reducing its mass to under 0,3Msol. Then it would not only burn slower, but also be fully convective - greatly extending its lifespan. Very low mass main sequence stars can potentially burn for trillions of years.

Re:We're all going to dieeeeee!!!!

[Anonymous Coward]

Some have argued with me that an expanding sun would just push the planetary orbits outward.

Through what mechanism? Reverse gravity?

The only way I can think of for an expanding sun to push the planetary orbits out would be a shock wave, which isn't so much going to push out your orbit, as simply scatter things in random directions that may or may not end up in stable orbits -- in fact, they may or may not still be in one piece.

The orbits aren't simply going to get bigger with the sun, because any force acting to push the planet outwards would be catastrophic.

I haven't seen a definitive answer either way.

What kind of 'definitive answer' to an incredibly stupid idea not founded in physics would you require?

Re:We're all going to dieeeeee!!!!

[Trogre]

Pretty sure that's wrong.

Orbits only depend on mass, not density. So assuming the actual mass of the Sun doesn't change when it goes supernova then our orbit won't change.

Likewise, if the Sun were replaced tomorrow with a black hole with the same mass, it would be the size of a small town but none of the planets' orbits would change. Although we would freeze to death.

Re:We're all going to dieeeeee!!!!

[Rei]

Surprisingly enough, it doesn't really matter what you siphon off. In a star the mass of our sun, there's relatively little inflow of new fuel into the core. Smaller stars are fully convective, in that everything can cycle through the core. So just by simply "lightening" the star by any means, down to a red dwarf (note: not a brown dwarf!), you let all of that new fuel get in. Also, the higher mass of the sun increases the reaction rate in the core, so reducing the mass slows that down significantly. And red dwarfs are strictly hydrogen-burning; there's never a helium flash, no triple alpha process.

Red dwarfs never turn into giants. Instead, they're predicted to evolve into blue dwarfs. Although since it takes orders of magnitude longer than the age of the universe for this to happen, there are no blue dwarfs in the universe yet to observe!