Astronomer Answers Cosmos Questions

I'm Jackie Faherty from the American Museum

of Natural History.

Let's answer your questions from the internet.

This is Cosmology Support.

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@EagleJomeur asks, Hey Siri,

how old is the universe?

The universe is roughly 14 billion years old,

and we get to that answer by looking out into the cosmos

and seeing the most distant things that we can.

The most distant thing in the observable universe

is the Cosmic Microwave Background radiation.

That's the signal of the Big Bang.

And right behind me, we have a representation

of what the Cosmic Microwave Background

radiation looks like.

Bluer colors or redder colors,

showing tiny temperature fluctuations

for what might have been going on

about 13.8 billion years ago.

@Purposefullylit asks, So did we decide if 3I Atlas

is a comet or an alien ship at this point?

I'm trying to see if I need to get my life together.

You need to get your life together.

It's just a comet.

It's not an alien ship.

3I Atlas is one of three objects that were discovered

that have a velocity that suggests

that they are not gravitationally bound to the sun.

They didn't come from the leftover material

that is in our solar system,

which is where the majority of our comets come from.

The first one was 'Oumuamua,

the second one is called Borisov.

And then there's 3I/ATLAS.

'Oumuamua came in and had a composition

that was most like what we would call an asteroid.

Borisov grew a tail

like we would usually see happen with comets

as they get close to the sun, they're icier,

and so you see a nice, beautiful tail as they get hotter

and closer to the sun.

3I/ATLAS arrived,

and all the imagery that we've seen thus far

indicates that it's got a tail like a comet.

So, 3I/ATLAS is still a really exciting object,

even if it isn't the alien ship that's gonna take everybody

to a different place.

3I/ATLAS is an object formed out of the material

from another solar system.

@M5Defence asks, Is the universe infinite?

In an infinite universe, it's infinite in all directions.

Lines of light stay parallel forever,

we refer to as a flat universe.

In a finite universe,

the structure would have to curve back on itself.

So it could be a curved structure,

like a spherical structure,

or it could be open on either sides like a saddle.

Studying the shape of the universe is a major aspect

of astrophysical research.

All we're really referring to in this case

is how light as it's moving,

is moving either parallel or it's curved.

So our current thinking now suggests

that we live in an infinite universe.

@TBG3963 asks, Are we living in a multiverse?

Yes or no?

I can't answer that yes or no because nobody knows.

Is it possible?

There's nothing I can tell you

that says that it is impossible.

So if you could, for instance,

get to a point where you saw our universe

from a bird's eye view,

could you see other universes out there

that had their own big bangs that started them?

That is a possibility and one that scientists look into.

That's not answering the question though,

if we live in a parallel universe

where there's multiple versions of every scenario

of every day you've ever lived,

this is simply, are we the only universe that is,

or is it possible that there are many out there?

And the answer to that question is maybe.

Okay, I'm [beep] Irish says, In 'Interstellar,'

why didn't approaching the black hole

cause Spaghettification?

Spaghettification is the idea that

as you get closer and closer

to something that's very, very massive,

the part of you that's approaching it

gets yanked with a force so big

that it starts to pull you apart.

And if you've watched the movie Interstellar,

Matthew McConaughey's character enters the event horizon.

The event horizon is the point of no return.

You have to get closer and closer

and closer to the singularity

or the center of that super massive black hole.

And because it's a hundred million solar masses,

he has to get way closer to the center of the singularity

before he feels that spaghettification.

Doesn't mean he wouldn't been feeling something,

he would've been feeling something,

but he wouldn't have been spaghettified.

Just remember the difference

between a super massive black hole

versus a stellar-mass black hole.

Very different gravitational pulls on your body.

Voodoomikvah asks, What's at the center of the Milky Way?

A super massive black hole,

which we call Sagittarius A*.

Also at the center of our galaxy,

there's gas and there's some dust.

I think of it like Metropolis or Times Square.

It's where a lot of material is congregating,

but all of it is kind of surrounding

this super massive black hole.

OMBX from Reddit asks, What came first?

Stars or galaxies?

The short answer is stars will come first.

Stars are the components of galaxies.

The first stars,

because they were basically just hydrogen,

were really large objects, probably a hundred times the mass

of our own sun.

And those didn't live for very long

because they're so massive.

And so as they blew up, they created the next generation

of materials that could come together to make more stars.

And as more stars formed, they clumped together.

And those clumps as they came together, formed galaxies,

and the galaxies then formed together

and they make galaxy clusters

and all of it comes together to make the cosmic web

that we know and love and live in today.

Bradley_Marques asks,

What is the largest single structure

discovered in the universe?

The largest structures that we know of

are roughly a billion light years across.

And what they are

are these gigantic walls of galaxies.

So the image that's behind me is from a map

that's been made of the Sloan Digital Sky Survey Galaxies.

It's a telescope that was in the United States,

and it measured how far away all the galaxies are.

It's color-coded by their density.

And there are some structures

that we can tell are all linked together,

where the galaxies are all held together

into a coherent structure.

And we call it the Sloan Great Wall.

And for many years that was the largest structure,

but now there's a couple of others

that are in competition for it.

They each stretch a billion light years across.

The Milky Way is a part of its own structure,

and we call that Laniakea.

Astronomers have looked at that structure

and seen a couple of things.

One, it kind of looks like a spiderweb

with filaments that are coming in and weaving around.

Those filaments are made of galaxies.

And then in the gaps between them,

you can see there's voids.

Much of this is being shaped by dark matter,

so this web, this structure,

which is the hierarchical map of the universe,

is carved out by material that we can't even see.

DJAnym wants to know, What exactly is dark energy

and dark matter?

When you look out across the cosmos,

you see the galaxies clump together.

But in studying the way everything moved,

we realized the stars in the galaxy

were orbiting in a way we did not fully understand.

Ones on the outside were moving faster

than we thought they should be.

Same thing with galaxies.

Huge clusters of galaxies were being held together

seemingly by nothing.

Some gravitational thing

that was giving off no light whatsoever.

And we dubbed it dark matter.

Dark matter has the same gravitational properties

that you and I have,

but it gives off no light, so we cannot see it.

And one other thing we discovered

is that the universe has been expanding.

And not only has it been getting larger,

it's getting larger, faster and faster.

And we weren't sure what to make of that either.

But when we realized that the most distant galaxies

are way farther away than we thought they should be,

we had to give a name to that,

to this mysterious force

that was driving our accelerating, expanding universe.

And that has been called dark energy.

So between those two, dark matter and dark energy,

they make up roughly 95% of the mass budget

of the whole universe.

Here's a question from the Astronomy subreddit.

How do you think the universe will end?

The universe is expanding,

and it's accelerating as it's expanding.

So things are moving farther away from each other.

If you wait long enough,

everything gets farther and farther

and farther away from each other.

New stars can't form.

The stars that are there will just peter out,

which means the heat,

what we call the entropy of the galaxy,

will just start to slowly dissipate farther and farther down

and it just becomes a frozen, dark cold world

where you can't see anything.

That is one and maybe the most likely scenario

called the Heat Death or the Big Freeze.

And in alteration of that,

this same dark energy accelerates the expansion,

pushing things farther and farther and farther away,

even to the interiors of things,

galaxies themselves pushed apart from each other.

All the gas, all the molecules,

the protons, the neutrons, the quarks,

it all gets decimated and eviscerated by this force.

We call that the Big Rip.

And then the third option

is that the volume of space hits the boundary.

That there is some point where we accelerate out

and that gravity takes us back in.

And when it does,

the universe shrinks back down to a singularity point

and that singularity would be the end of the universe.

And we call that the Big Crunch.

While all of these are scenarios

that are gonna take the universe out,

you do not have to worry about this right now.

Each one of these is trillions and trillions.

A Google number of years.

In the distant, distant, distant future.

I'd be way more worried about taking care

of our own planet right now

than how the universe is gonna take out the universe later.

Bluehairedhero asks, How do asteroid belts stay a belt,

wouldn't gravity pull all the asteroids together?

Great question.

I'm gonna answer that with a little Show and Tell here.

In front of me,

you might mistake them for just general rocks,

but they're rocks from space.

I have one here that is from a collision

that's called Allende,

and I have a second one from a fall that happened in Kansas.

Both of these are from asteroids.

The asteroid belt exists in a location

between Jupiter and Mars,

as shown in the image behind me

with all of the green dots that are out there.

This belt is not very dense.

It was probably a planet that wanted to form,

maybe Mars-sized or smaller than Mars' size,

but it's close to Jupiter.

Believe it or not, but you could fit the entirety

of all the other mass in the solar system aside from the sun

inside of Jupiter.

Jupiter has a very large gravitational pull.

As a result, it's wouldn't let a planet form

in that vicinity.

It would just gravitationally pull it apart.

But every single movie you've probably ever seen

that shows a spacefaring person

traveling around an asteroid belt has done it incorrectly.

You're not gonna dodge and weave all of these rocks

surrounding a belt.

There's huge gaps.

You can pass one of these rocks

and not see another one for a significant amount of time.

WritingConsistent834 asks, If an alien

with a very, very strong telescope

looked at the earth from one million light years away,

would they be seeing how the earth looked then?

Meaning how it looked a million years ago.

And the answer is yes.

Behind me there's an image of the Milky Way

with a grid around it

that is a million light years in radius.

And if there was a planet at the edge of any of that

that was looking towards us,

you would see the earth in an Ice Age.

You wouldn't see technology.

You would see megafauna.

If you were to go 66 million light years, even farther away,

a giant asteroid would be hitting the planet

as dinosaurs were having their last big moments.

This applies even in our own solar system.

We're a little over seven light minutes

away from the sun,

so it would take us a little over seven minutes to know

that something had happened

because it takes time for the light to leave the object

and arrive at your position.

at2wells asks, Why are sunspots black?

Sunspots are black because they represent

a slightly cooler temperature

on the surface of the sun.

So the sun is very magnetically active,

and sometimes it, for lack of a better expression, it burps.

When it does, it's spitting out some material,

and the surface might be representative

of a strong area of magnetic fields.

And it doesn't have as much convection

or the ability for heat to leave the sun,

which is why it looks to be a darker color.

And the sun does go through a cycle

where you see lots of sunspots to way less sunspots.

When you get more sunspots, you also get more of these burps

where more material will leave the sun,

come towards the earth and we can have geomagnetic storms

that cause fun things like the Aurora Borealis.

Here's a question from the NoStupidQuestions subreddit.

Would a solar flare destroy the internet?

The answer to that's probably a little bit complicated.

It wouldn't destroy the internet.

It's hard to destroy the internet,

but it could cause quite a bit of technological damage.

It's a very active star,

and sometimes it has coronal mass ejections

that come off of it.

What we're showing you is a big one.

It was called Bastille Day,

and it sent a whopping amount of charged particles

towards the earth.

The earth though has a very protective boundary,

which is this blue magnetic field

that you can see surrounding the earth,

and that helps us a lot.

Our magnetic field ends up cascading the plasma

down across the earth, centered at the poles,

which is why you can get these gorgeous light shows

closer to the northern or southern latitudes.

Also, this energy that comes from the sun

that interacts with our planet can overpower a grid

or can actually hit some of the satellites

that are orbiting the earth.

What we do now is we turn the satellites off

when we suspect there's a major magnetic storm happening.

iamedak asks, What is the difference between dwarf planets

and other planets,

is it just size or are there other factors?

The dwarf planet definition came in the early 2000s

when astronomers voted

on a new definition for the word planet.

And the object that really made everybody vote on it

is Pluto.

So the difference between a planet and a dwarf planet is,

are you dominating your area or not?

Jupiter for instance, it's got an asteroid belt around it.

It's got nearly a hundred moons around it.

Jupiter is dominating its area of the solar system.

Pluto just doesn't do that in its area.

And so for that,

it got demoted to dwarf planet status.

Another clear quirk about Pluto

is you can see all of the other orbits

of the main planets of the solar system.

They really form a plane,

a nice plane with a little bit of deviation,

but a nice plane around the sun itself,

but Pluto's off by tens of degrees

from the orbit of all of the others.

And so as it goes around,

it looks like it's off kilter

from the rest of the solar system.

So that was always a striking quality of Pluto

that made people feel a little less comfortable

with calling Pluto a planet

versus this new designation for it, which is a dwarf planet.

noblepups asks, What would happen

if two stars merged together?

It's not that easy to get it to happen.

Gravity is more interested

in getting the objects to orbit each other.

Small stars can do it

and it can be a nice merger,

an interesting little explosion.

It will be an explosion.

The bigger the star

or the more massive the objects that are merging,

the event gets crazier and crazier.

You can get, for instance,

two high mass stars to slam into each other.

And when they do,

they give off an enormous amount of energy.

So much so that you might get what's called

a gamma-ray burst,

which is the most energetic kind of explosion

that we see throughout the universe.

And famously we saw two neutron stars merge with each other

and the result was a wobble

in the entirety of space-time

that we could detect from here on earth.

@RachelinCanada asks, Wait, there are rogue planets now?

Yes, or at least there's a word that we use

to describe objects that are really low mass,

wandering the cosmos by themselves without a host star.

Maybe they got ejected from their home planetary system,

maybe they formed that way on their own.

But what we know is that there's Jupiter-like planets

that are wandering around.

The image behind me is showing the night sky,

but then we can actually show you with these blue circles,

the locations of stars where we found planets around them.

But then some of those blue circles

are gonna be surrounding nothing

because they are freely wandering dots in the sky

that are rogue worlds.

We actually think right now

every star has at least one planet, if not more.

So, finding planets is commonplace.

How common rogue planets are

is an open question in astronomy right now.

DWRedd asks, Is there any possibility

of having non-spherical planets out there?

By definition, by how the International

Astronomical Union defines them, need to be round.

You can be a little bit oblate,

meaning pulled apart a little bit on the sides,

but for the most part, by our definition,

you're supposed to be round.

There's a lot of objects out there in the solar system

that aren't round.

Here is an image for you to see, it's called Bennu.

Bennu is an asteroid.

We've actually gone to Bennu, landed on it,

taken a sample and brought it back.

But you can see it's quite an irregular shape.

When you go up to it,

it looks like it's a conglomeration of a lot of rocks

that have slammed into each other.

Those kinds of structures we see

throughout the asteroid belt.

You can see them even in tiny moons like the moons of Mars,

which are called Phobos and Deimos.

But for a planet to be called a planet,

you need it to be round.

@ThePhysicsMemes asks, Is there a spot

where the Big Bang happened?

Do we know where it is?

Is it the center of the universe?

One of the things that people have commonly through time

wanted to think is that there must be a center.

Maybe the earth was the center of the universe.

That was a thought process

before we really understood that we went around the sun.

Similarly in cosmology,

one way to look out into the universe

is to feel that there must be a center

'cause in all directions it looks like we have some homogeny

to the way that the galaxies are laid out,

but every single planet with a little earthling on it

or another species on it

would be looking out and thinking the same thing.

There is no center to the universe.

Everything is a part of the exact same

extremely large structure.

We're on the surface of a balloon.

The Big Bang is when the balloon started to blow up.

And then as it did, everything started to expand out.

The space that you're in right now

came from that same moment.

We live on the outside of the balloon though.

The outside of a balloon has no center.

It's a surface that is surrounding a material.

It's uniform for everyone in each direction.

FrankCyzyl asks, How do we know the shape of our galaxy?

No one's been outside to take a look.

The image behind me shows you what we think

the galaxy probably looks like,

and that's based on observations

that we have done from Earth.

Then we can look beyond our galaxy

and start to see the shapes that they have

and infer based on what we see.

We likely have a shape akin to a spiral.

Our best estimates, the galaxy is 150,000,

200,000 light years across,

but then only like a thousand light years thick.

It's compact. Are we definitely a spiral?

There's no definites on this,

but observational evidence

from looking at the way the stars move

and how gas and dust clumps,

indicates that we're a spiral galaxy.

@regastriga asks, What are the different types of stars?

Size and temperature really differentiate them.

So, the highest mass stars

called O Stars or B Stars.

And then there's A stars which are medium-sized stars,

and then there's stars like our sun, an F or a G star,

or even a K star.

Then it starts to get into the low mass stars

and those are the M stars.

And then you enter a regime

where you're not even talking about a star anymore,

but it probably forms in a similar way.

Some people call them failed stars.

There are objects that don't have enough mass

to get hydrogen burning at their core

to get a nuclear engine going.

And we call those things brown dwarfs

and they get the letters L, T and Y.

hanyzezo58 asks, Are super-Earth's real?

Super-Earths are real,

but I think they sound more exciting than what they are.

A super-Earth is a planet

that is bigger than the Earth is.

Sometimes they're also called mini Neptunes,

which probably doesn't sound quite as exciting

as super-Earths.

A super-Earth will be about twice the radius of the earth

and you can fit probably two to 10 earths inside of it.

And as we've scanned the cosmos,

the most common kind of planet that we've been finding

has been this super-Earth-sized planet.

And it's intriguing

that we don't have one in our solar system.

And astronomers never like to feel like

our solar system is special in some way.

So either we lost our super-Earth, or there is some concept

that there's a ninth planet beyond Pluto.

justyaboytee asks, Why is the night sky dark?

The short answer is because

the universe is kind of infinite.

This question is also something called Olbers' paradox.

If every line of sight

that you can point your finger at in the sky

lands on a star,

why isn't the night sky endlessly filled with light?

So while nearby stars, you can see really well,

as you get farther and farther

and farther away, the light,

it just takes longer to reach us from those locations.

And at some level,

it gets shifted to a wavelength that we can't see.

Bring a telescope in, then you can see more.

So for instance,

the Hubble Space Telescope famously took an image

where it stared at a seemingly dark patch of sky

continuously for several days,

and it was filled with galaxies, lots and lots of galaxies.

But that kind of ability to see

is not within the human capacity.

We are just not that sensitive to light.

Here's a question from Quora.

How many stars are visible from Earth?

So if you're in the Northern Hemisphere,

you've got maybe 4,000, 5,000 stars available to you

from the Southern Hemisphere.

So maybe like 9,000, 10,000 stars in total,

that the best conditions on planet Earth,

best eyeballs that we can possibly put out there

could actually see.

So what we can bring up here is a small sample

of roughly 350,000 stars that we have mapped,

that we know where they are and how they're moving.

You can't see them because your eye

is just not sensitive enough to be able to see these stars.

Light pollution is making it more difficult

for you to see them.

Your eye makes it difficult for you to see.

I would just encourage everybody to try and preserve

their nighttime sky.

This is the best view that you're ever gonna get

of what's out there in the cosmos.

So those are all the questions for today.

Thanks for watching Cosmology Support.

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