If I have seen further....the nose, the moose and the telescope.

“So it wasn't really until Galileo got his hands on a telescope that anyone really understood anything about space?”

The telescope was a huge advance but one of the most famous astronomers of all time, Tycho Brahe, died in 1601, just seven years before the telescope was invented in Holland in 1608.

“What was he famous for?”

As well being the worlds best astronomer four hundred years ago, he is also famous for having a magnificent moustache and loosing part of his nose.

“That's a bit careless, how did he do that?”

He had a duel in on 29th December 1566 with a Danish nobleman by the name of Manderup Parsberg and lost the end of his nose.

“What his fighting over, some woman I suppose?”

No, would you believe it, they were fighting to settle and argument over who was the best mathematician. Tycho Brahe was probably right about being the best mathematician but his sword skills were clearly not quite so sharp.

“So he spent the rest of his life without a nose?”

No he had a new one made of silver and wax.

“That's a bit weird isn't it?”

I presume that was what you did back then when someone sliced off your nose, but Tycho was certainly an unusual character. At one stage he had pet moose that he brought along to a party at the castle of Landskrona in Sweden. The moose apparently drank so much beer it fell down the stairs and broke its leg and died shortly after. Despite these series of unfortunate events, Tycho became famous across Europe for his talent in making extraordinarily accurate astronomical records of the positions stars and planets. Remember Johannes Kepler I told you about who worked out how the planets move? Well, Kepler was Tycho's student and he used all these measurements to produce his laws of planetary motion.

“How did he make all those measurements without a telescope?”


He used his eyes along with a variety of instruments like the sextant and quadrant to help measure the position of the stars. He didn't believe in the ancient Greek view of the universe with the Earth in the centre or the new outrageous Copernican notion of the Earth moving around the Sun. It may not surprise you to know that this slightly larger than life character believed most strongly in his own theories. His theory had the Earth at the centre but the rest of the planets moving around the sun which in turn moved around the Earth. This was as close to Copernican thinking as you could get without getting excommunicated by the Church but it was also wrong. He had great faith that his young student Kepler, with his mathematical abilities, would be able to use Tycho’s own huge volumes of measurements of planetary positions to prove his own theories right. He fortunately died before Kepler showed something completely different.

“But the telescope must have changed things completely.”

It certainly did, it also helped to finally separate astronomy from astrology.

"I thought you said that astrology was all rubbish."

I did and it is, but hundreds of years ago people wanted their fortunes told just like they do today. The astronomers of the day like Tycho Brahe had to make predictions to get paid. They had become so good at predicting the movements of the planets and eclipses that ordinary people and a few kings as well, assumed they could predict anything which of course they couldn't. But just like today, as long as they were fairly vague in their predictions no-one seemed to mind if they didn't come true.

"So how did the telescope change things?"

By making astronomy into a science. A lot of famous names we've already met designed new types of telescopes, like Johannes Kepler and Isaac Newton. Newton developed a totally new type of telescope based on mirrors rather than lenses and the biggest light telescopes today use mirrors to collect and focus light. As bigger and better telescopes helped astronomers see fainter and more distant objects, the size of the known universe steadily grew.

“So how far away can we see now with the best telescopes.”

With telescopes like the Hubble space telescope, galaxies have been seen that are up to 13 billion light years away. The light from these galaxies has been travelling for so long that some of these light beams started their journey just 700 million years after the universe was formed in the big bang, . From these distant galaxies we can look into the past and tell what the universe was like when it was very young.

“So you can see into the past with telescopes, but not into the future.”

Exactly and deeper into space. In just four hundred years mankind's understanding of the universe has stretched from the solar system to galaxies billions of light years away. Isaac Newton once said, 'If I have seen further, it is by standing on the shoulders of giants', but you could change that to say 'If man has seen further, it is because Newton developed the reflecting telescope.'

Little green men and Black holes

"Is a star completely blasted into dust in a supernova?"

No there is usually a core left behind and this is where the story gets interesting. Last time you asked a very intelligent question.

“Did I?”

You certainly did, you asked what stops gravity collapsing a star into nothing.

“..and you said it was the charged particles in atoms pushing away from each other like the poles of two magnets.”

Very good, you were listening. Well, that pushing effect which scientists call electron degeneracy is true up to a point.

“Electron degeneracy? What a great name for a rock band.”

Rock band?

“Rock, a new type of music, invented 50 years ago. You definitely need to get your entertainment circuits updated Albert, anyway you were telling me about gravity.”

Ah yes, gravity well if it gets too strong even the forces inside atoms aren’t strong enough and the electrons and protons in atoms get crushed together to end up as neutrons. Neutrons are not charged so can be squeezed together very tightly. A spoonful of pure neutrons would contain billions of tons. These dense neutron remnants are called neutron stars.

“So neutron stars must be tiny?”

They are. A neutron star with twice the mass of the sun might be only 15 miles across.

“So how can scientists see something that small thousands of light years away?”

When they first discovered them they thought they were alien radio stations. I told you earlier about radio telescopes. Well an astronomer Anthony Hewish from Cambridge University became interested in radio waves coming from stars. In 1967 one of his students, Jocelyn Bell, discovered a celestial radio source giving out regular radio pulses every 1.3373011 seconds. It was like radio-lighthouse in space.

“It wasn’t really a radio-lighthouse was it?”

No, but it was initially called LGM-1, short for Little Green Men because it seemed so fast and regular that an alien radio station seemed as likely as anything other explanation. Then they started finding more and more of them all over the galaxy, LGM-2, LGM-3, LGM-4. If you convert the radio signal into sound this is what a pulsar sounds like.

“So the universe does have a ticking clock then, like Newton said.”

No, it just has lots of spinning neutron stars. Like most things in space, the sun, the earth and the rest of the planets, neutron stars spin. And like ice skaters that spin faster as they pull their arms inwards, these solid lumps of matter spin faster and faster as they contract. You end up with a very small, very dense, star spinning around so fast that it can do a complete turn in a couple of seconds or even a fraction of a second. With each spin they give out a flash of radio-waves with every rotation which is why they are now called pulsars.

The Hubble telescope is so good that it has taken pictures that show the spinning of these stars.

“Are you serious?”

Oh yes take a look at this video. These are real pictures of the the supernova seen in the year 1054. The explosion left a cloud of gas and there is a pulsar in the middle of it. You can see the rotation and the ripples coming away from it. That’s the beauty of science, if you get it right everything starts to link together and make sense.

“I’m getting to see why you like science so much Albert.”

If you thought pulsars were interesting I have another surprise for you. Even stranger, and the only thing in the universe that we photons have to fear, is a black hole. They also can be created from exploding stars. If a collapsing star is a bit bigger than a neutron star, then the gravity will crush it to an even small size and create black hole. Like so many things in space, understanding black holes is all about gravity.

"Our friend Newton again?”

I don’t think Isaac would ever have imagined something like a black hole. In fact neither could I. A colleague of mine, Karl Schwarzschild, showed the my theories showed they could exist but I thought it was just a quirk of the equations. He even managed to do these calculations while he was serving in World War I calculating trajectories for artillery shells.

“Black holes and artillery shells?”

Well they both have to do with gravity but the gravity in a black hole is so strong even light can’t escape.

“Which is why they are black.”

Precisely. Here is how to make a black hole. Take the Earth and squeeze it into a ball less than an inch across and run as fast as you can. Most black holes are much bigger than that of course. There is probably a massive black hole in the centre of this galaxy, the milky way, which is about 10 million miles across. As long as the stuff inside is dense enough, gravity will do the rest. For all their mystery, the properties of black holes are still understandable in an apple falling way.

"Hmm, can't quite see how."

It's not as difficult to understand as you might think. You know that the gravitational force of the Earth stops you from throwing an apple into space.

"Of course, that's how Newton got the idea in the first place."

Exactly, if you throw an apple into the sky it falls back down again. Earth is therefore an apple-hole; apples cannot be thrown fast enough to escape the gravity of the Earth. Earth is also a bird-hole; birds cannot fly fast enough to fly into space. It is also an aeroplane-hole. To escape from the Earth you need a space rocket travelling at 25,500 miles an hour, any slower and the rocket will not be able to overcome gravity. Now imagine gravity getting stronger and stronger. The rocket will have to go faster and faster. The fastest thing in the universe is light and I’ll explain in a little bit why nothing can travel faster than us. So a black hole is a photon hole because photons cannot go fast enough to escape from the force of the gravity, in just the same way the Earth is an apple hole, bird hole and aeroplane hole.

“That makes sense.”

A long time before I invented relativity someone had already imagined that black holes could exist.

“Who?”

A Frenchman Pierre Simon de Laplace used this same argument in the year 1798, the year we've just reached, to predict that if a star had enough gravity it would stop light from escaping so become what he called a black star. It seemed such a crazy idea everyone ignored until I started coming up with just as crazy ideas.

"If you can't see black holes, how does anyone know they exist?"

Even though you can't see the holes themselves, you can see the effects of these strange things on neighbouring stars. As matter gets pulled in, it accelerates faster and faster and gives off x-rays in the process, the same sort of x-rays that are used in hospitals to take pictures of bones. These x-rays are a very high energy photon but are invisible and can go straight through your body and out the other side.

"So how do they escape?"

They escape because they are released just before the point of no return as matter is being pulled at huge speeds into the black hole. A special telescope that can detect x-rays from space can tell you where black holes might be. The constellation Cygnus, where we are coming from, contains the first detected object that might be a black hole.

"So what's it called? Vlad the absorber?"

You've been reading too many comics. No it ended up with a very boring name, X-1, because it was the first x-ray source detected in the constellation Cygnus.

“That’s the constellation we came from!

It certainly was, but luckily for us it was 5000 light years in opposite direction to the one we took towards Earth. So aren't you glad you ended up on this journey with me rather than being eaten up by a black hole.

"Oh, yes, but there is a lot space out there ahead of us and it all looks pretty black to me."

Exploding stars and why everyone has a little star quality

“Albert, quick look at that amazing star. I can't believe it's shining so brightly.”

That star isn’t shining, it’s exploding with style. That’s how some stars die, in a blaze of glory where they can outshine a whole galaxy for a few days or weeks That’s called a Supernova. You are very lucky to see one as they don’t happen everyday, you are also lucky it was a long way away.

"How often do these supernovas happen?”

In our galaxy, the milky way, only a few stars have exploded that violently while we’ve been travelling for the last couple of thousand years.

“Couple of thousand years? Rubbish we’ve been gone hardly anytime.”

Strange isn’t it, that time doesn’t do what we expect. That’s where I disagree with Newton, I don’t think the universe has a ticking clock that tells the actual time. Time only exists to stop everything happening at once.

“What a strange way of looking at things.”

One day I’ll explain my theory of relativity to you. Then you’ll really know how strange a place the universe is. Anyway do you want to know about exploding stars or not?

“Oh, yeah, sorry.”

Well the earliest one the humans saw and wrote about was in the year 185 AD when Chinese astronomers discovered a new star that slowly faded. The brightest one ever seen was seen on Earth in May 1006. After that there others in 1054, 1181, 1572 and the last one seen from earth from this galaxy was 1604 which is probably the one you are looking at now.

“There hasn’t been one since?”

Oh there probably has been quite a few, but the light just hasn’t reached us. Don’t forget the Milky Way is almost 100,000 light years across. The light from a supernova happening right now half way across the galaxy won’t reach here for 50,000 years.

“Will the Sun blow up like that?”

The Sun is too small to explode. Only very big stars explode like that.

“So what do stars like the Sun do?”

Smaller stars first swell up as they start to run out of hydrogen and then start cooling and shrinking. To know why that happens you need to understand how a star normally stays the same size. When a star is shining normally, the nuclear fusion reactions in the centre make a huge amount of energy and particles that are continually rushing out of the centre of the star. This balances the force of gravity so the star stops shrinking until it finds a balance and just shines away and stays the same size for most of its life. Think of a balloon, the stretchy rubber of the balloon is trying to shrink the star like gravity and the pressure of the air in side is pushing against the balloon.

“Until the air in the balloon escapes.”

That’s right the air escaping would be like nuclear fusion stopping so the star would star to contract. In a star the nuclear fusion reactions happen not just in the centre but also in layers further out. So it’s like having lots of balloons inside each other.

“Or like an onion?”

Yes you could think of it like the layers of an onion, either way when the centre runs out of hydrogen and the nuclear reactions start to slow down, this upsets the balance with gravity and the star starts to contract again. This heats up the next layer up which is still full of hydrogen. The outer parts get hotter as the fusion reactions move further from the centre and so they expand. The bits in the centre start combining the helium made by nuclear fusion into bigger and bigger atoms. This keeps going until the star gets bigger and bigger and ends up as a something called a red giant. By the time this happens to the Sun in about 5 billion years humans, or whatever the dominant species on the planet is by then, will have to find somewhere new to live.

"So what happens to stars after they swell up and become red giants?"

That’s where the size of the star comes in. Once all the atoms that can be used in nuclear reactions are used up, a normal sort of star starts to contract. There is no more nuclear fusion energy from the centre counteracting the pull of gravity. So they get smaller and smaller because of gravity. These star remnants are called white dwarfs, because even though they are still shining they may be no larger than the Earth which is tiny compared to your Sun. A piece of a white dwarf star the size of a sugar lump could weigh more than a ton.

“So what stops them shrinking to nothing?”

Despite all their gravity they can't keep on shrinking forever because all the charged particles in the atoms like electrons and protons start pushing away from each other if they get too close, a bit like two north poles of a magnet. This helps to balance the force of gravity but doesn't help the star to shine so it slowly cools down. White dwarfs cool down, shine less brightly and end up first as red dwarfs and then finally even colder brown dwarfs and finally cold lumps of dead stars.

“You said that large stars explode, what makes them so different?”

The biggest stars have a very different way of living and dying. A star ten times the size of the sun can be born from a cloud of gas and dust in only a few hundred thousand years because the greater the mass the greater the gravity pulling everything together. So it all happens faster. At ten times the size it will shine 10,000 times brighter than the Sun but last only 2 million years until they do what that Supernova just did. They live fast and die young.

“But why do they explode when smaller stars don’t?”

The short answer is that big stars have so much gravity that when the balance between gravity and nuclear fusion goes wrong the star can suddenly collapse crushing the centre which gets massively hot and explodes. When really large stars run out of hydrogen fuel for fusion reactions they can move on to fusion reactions with bigger and bigger atoms because they have much more gravity which makes the centre much hotter than a normal star. All these fusion reactions build up bigger and bigger atoms ending up with the formation of iron.

“Iron doesn’t explode does it?”

Not by itself. It’s when these big stars try to use iron atoms in fusion reactions that everything starts going very wrong. Rather than release energy, nuclear fusion reactions with iron, absorb energy. So rather than making the centre of the star expands to counterbalance the effects of gravity the centre of the star suddenly starts to collapse. The matter in the centre then gets squashed into a super-concentrated form and the gas around the centre gets blasted out into space. This cosmic explosion is a supernova, and for a brief time a single supernova can outshine an entire galaxy. In the process of exploding a huge variety of nuclear reactions happen which result in the formation of all the complicated heavy atoms that are even bigger than Iron.

Remember I told you that humans are mostly made up of just six types of atoms; carbon, nitrogen, oxygen, hydrogen, calcium and phosphorus. Well all these atoms, except the hydrogen, were made inside a star before it died. There are some even bigger atoms in humans and these would have made in a supernova explosion millions or billions of years before the sun formed

"So this huge explosion blasts into space all the new types of atoms the star's been making from nuclear reactions, but how does it get into humans?"

Well the remnants of these explosions become the gas and dust that makes up the next generation of stars and planets.

"So the planet Earth and all the people on it are recycled space junk?"

Every one of them is made up of little bits of recycled stars. It may be well hidden but there’s star quality in every one of them.

"Do they know that?"

Well the smart ones, like you, do. But remember exactly the same star quality is found in mosquitoes, earthworms and the ink in a Bic biro. So don’t be getting any grand notions about yourself.