Ever heard of white holes?
The Universe is big, and strange, and there’s a lot of stuff out there that works in mysterious ways. Astronomers spend their time trying to understand these workings so they can figure out the Big Questions: Who we are. If we’re alone. Where the Universe came from. Where it’s going.
One of our favourite resources on the web for finding answers to all your burning questions about space is run by Cornell University. It’s called Ask an Astronomer, and it has a database of questions sent in by curious readers, all answered by volunteer Cornell scientists.
Confused about what a singularity is? Or how to calculate distances between the stars? Or whether we’re viewing the near edge and the far edge of a galaxy at different epochs? The website totally has you covered.
It’s easy to spend hours poring through the answers, but if you’re looking for a place to start, here are five of our favourites.
What would happen if a supermassive black hole happened by Earth?
We’d all die, obviously, but could it happen? And what would the process look like?
This question was fielded by astronomer Christopher Springob, who explained that although it’s super-unlikely, it’s not entirely impossible that a supermassive black hole, usually found at galactic centres, could pass close to Earth if the Milky Way were to merge with another galaxy.
Based on a supermassive black hole weighing a million Suns, Springob calculated that we would start to notice something odd in the Solar System’s orbit around the galaxy at a distance of about 1,000 light-years.
“Once the SBH got within a few hundred AU (1 AU = distance between the Earth and the Sun) of us, it would start to seriously disrupt the orbits of the planets in our solar system, including the Earth. So we would very quickly either boil or freeze to death, as we’d either get too close to or too far away from the Sun.
“There are any number of different things that could happen to the Earth after that point. We could fall into the Sun. We could be thrown out of the solar system, but into some elliptical orbit around the SBH. We could be thrown *into* the SBH,” he said.
If we did end up falling into the black hole, the intense gravitational tidal forces would rip the planet to shreds first. Either way, though, we’d be long gone.
The Milky Way probably is going to merge with another galaxy eventually. The Andromeda is drawing ever closer, on course for a collision in about 4 billion years’ time.
But humanity’s expiration date is much shorter than that – we only have about 1 billion years left before Earth gets too hot for habitability. So you shouldn’t lose any sleep.
And, as Springob put it, “This is so improbable as to be hardly worth considering. But it’s still fun to think about.”
You can read the full answer here.
How would your weight change closer to the Earth’s core?
Many years ago, a Bronze Age Marvel comic sent characters to the centre of the Earth, where they became immensely heavy.
Science hasn’t always been comics’ strong suit, but the writer was probably operating under the principle that, as you get farther from Earth, gravity’s grip grows weaker, until you’re floating in the vacuum of space. So it stands to reason that the closer you get, the stronger gravity is, right?
Nooooo, says Karen Masters – and this is because the force of gravity depends not just on your distance from the centre of the Earth, but the mass enclosed within that distance. And it’s only the mass inside the radius of your distance from the centre of the Earth that affects the force gravity exerts on you.
“So, if you tunneled through the Earth to the centre, right at R=0 [the centre] there would be no mass enclosed, so there is no net force of gravity,” Masters explained.
This is, she notes, a bit of a simplification, but she provides some links for further reading in her full answer, which can be found here.
Can I buy a star?
This was all the rage for a while, but it seems to have died down now – which is probably a good thing. Short answer? No. You cannot buy and officially name a star.
As Lynn Carter points out, only The International Astronomical Union is officially allowed to name stars, and any organisation that says otherwise is lying to you.
“In fact, the companies that do this don’t even make an effort to communicate with real astronomers on the subject, they just keep a big book or spreadsheet with everyone’s name in it,” Carter said.
“Also, a lot of times the star you are given will be very dim, or even not visible to the unaided eye. A lot of people email us asking how to find stars that they have ‘purchased’, and it turns out that you need a telescope to see them, if you can even find the one dim star in a field of view full of other dim stars.”
You’re essentially just paying for a certificate, something you can do at home for free.
Star-selling got so predatory that the NYC Department of Consumer Affairs issued one company a big fine in 1998 for deceptive trade practices.
If you know what you’re buying and are totally happy with it, that seems fine to her, Carter noted – but you might enjoy it more if you pick a star that you can actually see and means something to you, and donate the money to a charity in your loved one’s name.
You can read her full answer here.
What is a white hole?
You’ve heard of a black hole, but what the heckers is a white hole? Well, pretty much what it sounds like – the opposite of a black hole. Where matter falls into a black hole and cannot escape, a white hole spews matter out, but nothing can enter it.
“A white hole is something which probably cannot exist in the real universe. A white hole will turn up in your mathematics if you explore the space-time around a black hole without including the star which made the black hole (i.e. there is absolutely no matter in the solution).
“Once you add any matter to the space-time, the part which included a white hole disappears,” she writes.
If a black hole has no mass, then it’s a singularity, she goes on to explain, and the only way singularities can exist in the Universe is if they were there from the beginning.
There’s nothing to suggest that the Universe could have included singularities when it formed, and even if it did, even the tiniest speck of mass would make the white hole disappear, so any white holes would be long gone.
You can read the full answer here.
What is the Universe expanding into?
We know the Universe is expanding. That means there has to be something on the other side for it to expand into, right?
Well, not really, says Dave Rothstein, although his explanation may make your brain hurt a little. He said that, if the Universe is already infinitely big, it isn’t really expanding at all. A more accurate way to describe its movement is stretching.
“What is happening is that every region of the Universe, every distance between every pair of galaxies, is being ‘stretched’, but the overall size of the universe was infinitely big to begin with and continues to remain infinitely big as time goes on, so the Universe’s size doesn’t change, and therefore it doesn’t expand into anything,” he explained.
But it’s a little trickier to explain if the Universe is, in fact, finite.
“If, on the other hand, the universe has a finite size, then it may be legitimate to claim that there is something ‘outside of the universe’ that the universe is expanding into. However, because we are, by definition, stuck within the space that makes up our universe and have no way to observe anything outside of it, this ceases to be a question that can be answered scientifically.
“So the answer in that case is that we really don’t know what, if anything, the universe is expanding into.”
So there’s two possible answers there: it’s either expanding (or stretching) into more space; or it’s expanding into a giant mystery that we’ll probably never know the answer to.
Rothstein goes into a lot more detail, so you should probably head on over to his answer and read the whole thing for yourself.