Download What is the biggest star? - University of Central Lancashire

EXPLORING LIGHT AND DARK EXHIBITION – CHOREOGRAPHY WORKSHOPS
Questions about the stars that were asked to choreographer Ruth Spencer by junior school pupils
in the Copeland area, and answered by University of Central Lancashire researcher Dr. Joanne
Pledger
What are the different colours in the stars?
That’s a really good question. If you look at a candle flame you will notice that the flame is yellow at
the top, but near the wick at the bottom it is blue, that is because it is hotter at the bottom. The same
idea applies to stars. The different colours tell us how hot the star is, the hottest stars are blue and
white and the coolest are red.
Is there a star called Bettlegaze?
I think you mean a star called Betelgeuse. Yes there is. Betelgeuse is a red star that is about 12 times
as massive as our Sun and it is in the top left corner of a constellation called Orion.
How does a star die?
A star can die in many different ways, it all depends on how massive a star is. For little stars like our
Sun the outer layers will be expelled from the star in a planetary nebula and the core will be left
which will become a White Dwarf. For more massive stars they get rid of their outer layers more
dramatically and end their lives as a Supernova explosion.
Is a constellation big stars or little stars?
Both. A constellation is a group of stars that make a particular pattern on the sky, they can be big
stars or little stars, it doesn’t matter and some stars may even be closer to us that others in the same
constellation – we simply can’t tell just by looking at them.
What will happen to the earth when the sun blows up?
When the Sun stars to die, it will expand into a Red Giant. At this point it will grow and “eat” the
planets closest to the Sun like Mercury and Venus. We don’t think it will eat Earth but because the
edge of the Sun will be much closer to us Earth will be much hotter and the water in the oceans might
boil and evaporate like it does in a pan or kettle.
Do you like studying stars? How did you start getting interested?
I do like studying stars. I started to be interested when I was young, just like you and I would often
look at the stars with my Dad, but it wasn’t until I was about 15 that I got my first telescope and
looked at planets too – that was very exciting and definitely got me interested even more.
What is the biggest star?
The most massive star we know isn’t actually in our Galaxy, it is in a nearby galaxy called the Large
Magellanic Cloud and is nearly 300 times as massive as our Sun! It is called R136a1 – not a very
exciting name.
Will there be a heaven when the world ends?
I honestly don’t know. There is a lot about Astronomy and the Universe that we don’t know which is
why it is important to keep asking questions and looking for answers.
If all the stars went what would be left?
Stars are very similar to people in the fact that as some die, others are born. In fact, when stars die in
explosions the material ejected into space will end up in a new star – like recycling, so it is hard to
imagine space without stars. But one thing is for sure, without stars, there wouldn’t be enough heat
in the Universe to support life on planets like Earth.
Once the sun expands will there be any planets left in our solar system?
Yes there will. Only the closest planets to the Sun will be destroyed, hopefully Earth will escape but
life on Earth will change.
What’s the blue coloured gas?
Do you mean why are stars blue? This links back to the earlier question and the answer is because
they are hotter than other stars like our Sun. Gases like Mercury (not the planet!) and Argon emit
blue light but these aren’t found a lot in stars.
Why are stars made of gas?
When the Universe was first formed it was mostly made up of gas and dust and the first stars formed
out of this gas by gravity compressing it into a ball. It is because they are gas that they undergo
nuclear fusion and create heat and light.
Is there a green star?
Stars emit light at many different colours, not just one. We don’t see green stars as our eyes just
don’t see them like that. When we see a star we see the blended colour rather than a single colour
which is why we don’t see green stars.
Why does the earth orbit the sun?
The Earth orbits the Sun because it started forming at the same time, out of the same material as the
Sun. When all the material came together to form the Sun it was rotating around the middle, and it
still is today but just as the Sun and Planets.
Will the sun explode?
No, the Sun will be stripped in a planetary nebula and the core will end up as a White Dwarf but it
won’t explode.
What's the smallest star?
The smallest a star can be is 0.08 times as heavy as our Sun (or 8%), if it is smaller than this then it
can’t get hot enough to undergo nuclear fusion so it can’t be called a star.
What's the biggest star?
The most massive star we know isn’t actually in our Galaxy, it is in a nearby galaxy called the Large
Magellanic Cloud and is nearly 300 times as massive as our Sun! It is called R136a1 – not a very
exciting name.
Why are stars all different shapes and sizes?
Stars come in a variety of sizes as it depends how much material there is in the gas cloud to begin
with – you can’t make a big star out of a little bit of material. However, all stars are roughly
spherical.
Is there a brown star?
This relates to an earlier question. If a star is too small to undergo nuclear fusion it is called a Brown
Dwarf, which is a failed star.
Is there any star that could, in collapsing into a black hole, destroy our own sun?
That’s a really interesting question. If a star massive enough was close to a star like the Sun then
when it collapsed to a black hole it could destroy the smaller star. However, there is no star massive
enough and close enough to our Sun, so it is safe from black holes
Do aliens exist?
Most likely yes! For life to form we need a set of specific conditions, but the Universe is a very large
place with lots of stars and planets so there is a high chance a suitable planet is suitable close/far
enough to its star to allow life to grow.
How many black holes have we had in our solar system?
None. If we had a black hole in our Solar System then chances are our Solar System wouldn’t look like
it does. A black hole forms after the explosion of a very massive star which would destroy things close
to it.
Will the world end?
Yes! The question is how and that is something we don’t know.
Has any planet other than Pluto been knocked out of our solar system?
Pluto hasn’t been knocked out of our Solar System, it has just been changed from a Planet to a Dwarf
Planet. This is to do with lots of things like its size and how it moves around the Sun – but it is still in
our Solar System.
Is a black hole a star?
No. A black hole forms after the explosion of a very massive star so is actually a stellar remnant (or
leftovers!)
When will the earth end?
I don’t know. We don’t know how the Earth will end so it’s hard to predict when it will happen. If a
large enough Asteroid hit Earth tomorrow it could destroy life on Earth (but as far as we know that
isn’t going to happen)
Is there another planet like earth?
Most likely yes. The Kepler Space telescope has found planets that are very very similar to Earth so
it’s just a matter of time until we find one just like Earth.
What do you think the straight walls on asteroids are?
Asteroids come in many different sizes and travel from all over the Solar System and beyond so they
can encounter, or be hit, by other asteroids that can change their shape and size.
How does gravity work?
That is a really good question, and there isn’t an easy answer. Gravity is what causes things to drop
to the floor when you let go, you to come back down to Earth when you jump, and the planets to
orbit around the Sun. It is the gravity between objects that controls the path they take.
What do Nova’s look like?
Do you mean supernova? A supernova is a huge explosion when a star dies, but a Nova is a when a
smaller star shed layers but not as powerful as a massive star. We often only see supernova as bright
points of light as they are so far away but the Crab Nebula was a supernova in our galaxy that now
looks like this:
http://www.nasa.gov/sites/default/files/images/430453main_crabmosaic_hst_big_full.jpg We can
see this much detail because it is in the Milky Way.
How does gravity pull the gases into one place?
In star formation, the gravitational energy is balanced by energy from pressure from the gas cloud
itself, but if the cloud is big enough the gravitational energy becomes larger than the pressure so
gravity pulls the cloud inward which eventually forms a star.
How can stars ignite when there isn’t any vacuum for it to ignite?
Stars ignite when the temperature is hot enough, and reaches millions of degrees at the centre the
atoms in the gas will ignite to fuse Hydrogen atoms together. You don’t need an external source like
you would to light a fire on Earth.
How big was the telescope in Chile?
The Gemini telescope in Chile was 8 meters in diameter, all the way across. We are not building
telescopes that are 30 meters in diameter so imagine what we can see with them!
How hot is the biggest star?
The biggest star is called R136a1 and is about 10 times hotter than the Sun on the surface, but is 9
million times as bright!
When the sun burns is it dying?
In a way yes, as soon as the Sun started to burn Hydrogen and “shine” it began using up its energy
which will run out at some point, but the Sun is not an old star and has a lot of life left!
How is the sun formed and how old is it?
The Sun formed like all stars do, from a cloud of gas and dust which came together under gravity.
The Sun is about 7 billion years old, about half-way through its life.
How do new stars appear?
New stars look exactly like all the other stars, what changes the way a star looks is its size, its mass
and how hot it is. Hotter stars appear bluer in the sky, cooler stars are redder.
When the stars die..what happens? Where does it go?
If a star is massive enough then when it dies it will explode as a supernova. It might not destroy itself
completely and the core of the star will be left, called a Neutron Star, but the rest of the star will be
ejected into space and will go on to make new stars and planets.
Does the sun’s temperature change everyday?
The Sun has sunspots on it but the number of these changes constantly which in turn changes the
brightness and temperature of the Sun, but only very slightly.
Is the amount of solar flare activity related to the age of the star? (teacher question)
In a way yes, the older the star (or more evolved) the more likely it is to shed its outer layers which
results in mass-loss events – kind of an extreme Solar flare.
Are stars always made out of burning gas?
Yes, the burning gas is their fuel source and without it they wouldn’t be stars. We know Brown
Dwarfs exist and are failed stars because they couldn’t get hot enough to burn their gas.
How do stars get really big?
A lot of them form that way, so when they form there is just more material to make them but some
stars can merge with each other so two smaller stars can make a big one.
Is there a limit to how many stars there can be?
That is a really good question. How many stars you get depends on how much material you start
with in your gas cloud. But at the end of the stars life it recycles that material by ejecting it into
space so it can make new stars.
Is the Wolf Rayet the smallest star? What is the smallest star you’ve ever seen?
No the Wolf-Rayet star is the inner layers of a star that used to be much bigger but it isn’t the
smaller stars ever. The smallest stars are about 8% the mass of the Sun.
Do all stars die?
Yes. Some may live for millions of years and others for billions of years but they will all die at some
point. How they die depends on their mass.
Is the sun on fire?
The Sun is undergoing fusion which is a nuclear reaction where fire is a chemical reaction that needs
Oxygen so no the Sun isn’t on fire, but it is very hot.
How many earths are there?
We are always looking for new planets using the Kepler Space Telescope and we have found many
that are similar, if not exactly eh same as Earth but I am sure we will. We predict that there are
millions of planets like the Earth in our own Galaxy and beyond.
How hot can a star get?
The hottest stars we know are around 10 times as hot as the Sun on the surface, but in the core in
the centre of the star the hottest stars are 40 million degrees.
How hot is the sun?
The surface of the Sun is about 6000 degrees but the core is a about 15 million degrees, so a lot
hotter.
How do stars make light?
Stars make energy by undergoing nuclear fusion and in doing so light, or photons, are given off. It is
these photons that make a star shine.
How do scientists know where to look for stars?
Just like planes or ships or cub scouts navigating their way around Earth, Astronomers use a similar
method to know where to look for a particular star or galaxy. We split the sky into a grid with lots of
squares so we know where to look at different times of the year.
Do stars become black holes?
Some do yes, the most massive, about 60 times as massive as our Sun will leave no core after
exploding and will collapse to a Black Hole.
How many stars are there? (some of the class thought 60, others thought 400 billion)
There are about 100-400 billion stars in our Milky Way alone, it’s hard to know an exact number as
we can’t see through the centre of the Galaxy to know what is on the other side. Also, we think
there are around 100 billion galaxies in the Universe so that is a lot of stars!
What colours can the stars be?
The colour of a star depends on how hot it is, the hottest stars are blue, the coolest stars are red.
How many Red Supergiant stars have been found?
That’s a really hard question to answer as we are always looking for new stars and it is hard to see
across our Galaxy to see how many there are. It’s much easier to see them in other galaxies, for
example M33 where we have found 189 Red Supergiants, but there could be more.
What different colours can stars be?
The colour of a star depends on how hot it is, the hottest stars are blue, the coolest stars are red.
How is a black hole made?
The most massive stars, about 60 times as massive as our Sun will leave no core after exploding and
will collapse to a Black Hole.
Where does the gas that makes the stars come from?
The gas that makes stars comes from the previous generation of stars. When a star explodes as a
supernova it expels all its contents into space and then this can clump into clouds which can then
make new stars.
Why are stars so bright?
Stars are bright because of their temperature. Think about if you heated up a spoon with a Bunsen
burner or flame, the spoon would start to glow. Stars have a lot of energy that wants to get out,
generally the bigger and hotter a star the brighter it is.
What is the same and what is different about different stars?
Different stars are different in every way. There are many different categories of stars so it is very
unlikely to find one exactly the same. The more we study our Sun the more detail we find but it is
hard to see this detail in stars much further away so we can’t see if they are the same or not.
Are all stars made of gas?
Yes, they are. It is the gas coming together that makes up the fuel for the star to star undergoing
nuclear fusion.
How long have stars been living?
A really good question, we think the universe is about 13 billion years old and the first starts would
have formed not long after the big bang, but those stars would have been a bit different than the
stars we know today. Stars themselves can live for millions or even billions of years depending on
their mass – massive stars live short lives whilst lower-mass stars like our Sun have much longer
lives.
What colour is the star that has lived the longest?
Red stars that are cooler and smaller than our Sun will live the longest as they don’t need as much
energy to keep them going.