It is only possible for us to precisely and directly measure objects 1000 light years away using telescopes. Therefore, astronomers use the cosmic distance ladder, which is a series of methods, to find the distance of far away celestial bodies. There are five different way used to find the distances of planets, stars, galaxies and more. The first way is using radar ranging to measure how far away objects in our solar system are. The distance between us and nearby stars, 100 light years away are measured using spectroscopic parallax. Main-sequence fitting is used to find the distance between the Earth and objects on the other side of the Milky Way galaxy, approximately 100,000 light years away. A method called Cepheids measures objects 10,000,000 light years away in nearby galaxies. Finally, the distance to galaxy clusters and objects further away than that are measured using Hubble’s Law equation of d=v/Ho. Radar Ranging is when a signal, such as a radio pulse, is fired at a nearby celestial object. This signal is then reflected back to Earth and by dividing the time it took for the pulse to be sent and received by two, we can work out the distance of the object. This method is one of the most accurate ones of the cosmic distance ladder. The spectroscopic parallax method uses the Hertzsprung-Russell (HR) diagram to measure the distance between Earth and a nearby star. Firstly, by using the different types of spectral lines in the star’s spectrum, astronomers can find where the star belongs on the x-axis of the HR diagram by determining the star’s spectral type. Next, astronomers work out where the star belongs on the y-axis depending on its luminosity (between I and V). A V classed star would have thick absorption lines on its spectrum. This is because the density of atoms in the outer layers of the star is high. However, a star classed as I would have very thin spectral lines due to the low density of the absorbing atoms. So by using where the lines of the plotted x-axis and y-axis meet, astronomers can work out the absolute magnitude of the star. By using this, and the apparent magnitude, the distance to the star can be worked out through the equation m - M = 5 * log (D/10). Main-sequence fitting also uses the HR diagram, but only is used for a cluster of stars. 90% of the stars in the cluster are on the main sequence because they are all gravitationally bound, located at the same distance from Earth and formed at approximately the same time from the same cloud of dust and gas. The method of main sequence fitting compares the apparent magnitude and the absolute magnitude of the main sequence for the cluster of stars. The vertical position of the main sequence of the cluster is adjusted so that it lines up with the main sequence of nearby stars. The distance is worked out by how much the main sequence of the cluster was adjusted. Cepheids are variable stars meaning they change brightness on a regular pattern. They were discovered by Henrietta Leavitt, an American astronomer, in the early 1900’s. Astronomers measure the pulsation period of Cepheids to work their absolute magnitude and therefore their apparent magnitude. By using the equation m - M = 5 * log (D/10) astronomers can work out the distance between Earth and nearby galaxies. Hubble’s Law states that the redshifts in the spectra of distant galaxies are proportional to their distance. In 1929 Edwin Hubble realised that the universe was expanding and estimated that it was doing so at a rate of around 65 km/sec/Mpc (known as Hubble’s constant). However, the exact expansion rate is still unknown. So by finding the velocity of a celestial body (by using the Doppler shift), we can use the equation d=v/Ho to work out the distance between us and the object.
In conclusion, the cosmic distance ladder offers a range of methods for astronomers to measure the distance of objects in the universe, whether in our solar system or outside our galaxy. Selina, Year 11 (Before we start, these are all only theories and would occur in billions of years time so no need to freak out!) There are 3 main theories as to how the universe will end, depending on which of these becomes dominant - gravity, entropy or expansion. 1 - The Big Rip - Expansion Wins The universe is expanding at an accelerating rate, therefore we can assume that at some point the universe will expand so fast that gravity cannot compensate for the expansion. This would result in everything, including atoms, being torn apart. Eventually, the universe would expand faster than light. As the speed of light cannot be exceeded by any particle, no particle would ever be able to interact with any other particle again, turning the universe into a strange timeless void. 2 - Heat death - Entropy wins In this (intense sounding) theory the universe continues to expand forever, and while this happens all matter slowly decays and spreads out, until it is all converted into radiation. The universe gets colder. The is eventually no activity in the universe as it has reached maximum entropy, which means that all energy as evenly spread out and the universe has reached equilibrium, and no work (energy transfers) can ever be done again. However, it may be possible to have a spontaneous entropy decrease after very long time, leading to a new big bang. 3 - Big crunch and big bounce - gravity wins If the universe's expansion stops, gravity becomes the dominating force - so the universe contracts instead of expands. As the universe gets smaller, it also gets hotter. 100,000 years before crunch, background radiation everywhere would be hotter than the surface of the sun. Eventually all black holes would merge into one black hole containing the entire universe’s mass, which then consumes the whole universe including itself!? The Big Bounce theory states the universe is in an infinite cycle of expansion and contraction. The fate of the universe essentially depends on the shape of the universe and the role of dark energy. Currently many cosmologists believe that the universe is flat and will continue to expand forever, so at the moment the most likely theory is thought to be the Big Rip.
Izzy, Year 11 The first thing to clear up is that you can’t actually hear anything in space as we can on Earth. The only way you would be able to hear anything occurring in space is if a supernova exploded really close to the Earth. Even then, it’s not the sound of the explosion that you would hear, it would be the sound of our own atmosphere being ripped to shreds as the debris and light pressure produced hit it. Then we’d all be dead. The reason why we can’t hear anything in outer space is because sound waves are transmitted as particles collide with each other. In space, there are none of these particles, because space is a vacuum. Actually, to be more specific, not all of space is a total vacuum (think of the stars and the planets, etc.), but interstellar space, the space between these massive objects, has so few particles that they will never collide into each other. This means that, for example, any sound produced from you hitting the side of a satellite without a spacesuit on (imagining that you aren’t already dead), wouldn’t reach your ears. However, if you did have a space suit on, and you hit your head against the side of the said satellite, you would hear the noise, as the waves could travel through the particles in your helmet. Similarly, it is possible to hear radio transmissions from other astronauts, as radio waves use electromagnetic waves, which, like light waves, do not require matter to travel. Once these waves reach your radio, the radio can convert the signal back into sound for you to hear through your helmet. However, after everything I’ve just told you, these electromagnetic waves are what actually enable us to ‘hear’ in space, to some degree. Various space probes have recorded electromagnetic vibrations which naturally occur in the vacuum of interstellar space. They do this by recording interactions between solar winds and our planet, as well as the rings of Saturn and Jupiter, and the moons Io and Miranda. When these recordings are sent back down to Earth, scientists can convert them into sounds, like the radios do inside the astronaut’s helmet. It can create eerie sounds like these, which were recorded at saturn’s rings: The deepest ever note detected in our universe was a B♭, which was detected from a supermassive black hole located in one of the cluster of galaxies in the constellation Perseus, 250 million light years from Earth. It’s actually impossible to hear the note as a human, as 9.6 million years is the estimated time period of its oscillations! As well as this, it is 57 octaves below the note ‘middle C’, which the note in the middle of the piano, which is far beyond human hearing range.
Eleanor, Year 11 All the matter that is known to us only accounts for less than 5% of the matter in the entire universe. About 27% is dark matter and 68% is dark energy. Scientists do not know what dark matter or dark energy is or how they work. They have just come up with many theories that still have to be proven. At the moment, scientists are unable to detect or measure dark energy and matter because they do not act like the matter that we know. Scientists only know 3 factors that prove that dark matter and energy must exist:
The gravity of normal matter is not strong enough to form complex structures such as galaxies. Stars would just be randomly placed with no order throughout the universe. Something else must be around normal matter with enough gravity to hold stars and normal matter together. Dark matter does not emit or reflect light as we are unable to see it or sense it. Places with a high concentration of dark matter bend light passing by. The only possible solution to this is something else that we are unable to detect. At the moment, scientists know what dark matter is not more than what it is. Dark matter is not cloud of normal matter without stars because it would emit particles that we would be able to detect. Dark matter is also not antimatter as antimatter creates gamma rays when it reacts with normal matter. As well as that, dark matter is not made up of black holes as it is scattered everywhere. We cannot measure or detect dark energy but we do see its effects. It is what causes the constant acceleration of the expansion of the universe and it is stronger than anything we know. Also, dark energy has to be becoming stronger and stronger. Empty space has more energy than everything else in the universe combined. Scientists have 4 possible theories on what dark energy could be:
So overall, no one actually has any idea what dark matter or dark energy is. We just knows that it has to exist otherwise many things in the universe would not be as they are. Considering scientists do not know how to measure or detect dark energy and dark matter, it could be a while till we find real evidence that they do exist and a theory is proven. Selina, Year 10 Outer space is not really a total vacuum. In fact, it is made up of gas and dust particles known as the Interstellar Medium. When a gas in the Interstellar Medium undergoes gravitational collapse, the gas particles have their own gravitational attraction and clump together in a cloud, or a nebula, if you speak fluent latin. When talking in the context of astronomy, nebulae aren't normal clouds - they are massive interstellar clouds made up of plasma, hydrogen, helium and dust. They are also known as 'star nurseries', because they are often where stars are 'born', or formed. An example of some famous star nurseries are the Pillars of Creation, in the Eagle Nebula. Lots of people, me included, are interested in nebulae because of their looks. They can be many shapes and sizes (although all of them are hundreds or millions of light years across) as well as a vast variety of colours. Most people recognise nebulae as being pink or red, but only one type of nebula actually is: an emission nebula. When a star forms inside a nebula, gas and dust squash together under their own gravitational pull. The clouds get denser, and the denser they become, the hotter they get. Eventually they become so hot that hydrogen in them gets ignited and new stars come to life. This is when ultraviolet rays are emitted and the entire nebula is lit up, resulting in a pink or red emission nebula. Orion's nebula is one of these. Apart from emission nebulae we have other types of nebulae known as the reflection nebulae; they are named like this because they do not emit their own light. Reflection nebulae only reflect the light from the nearby stars. These appear blue in colour. The interesting thing about this is that presence of reflection nebula means the presence of an emission nebula somewhere close. There is also another type of nebula known as planetary nebula. Despite the name, planetary nebulae have nothing to do with planets. A planetary nebula forms when a star similar to the size of our Sun starts to expand and becomes a red giant. The core of the red giant is heated so much that the star becomes very unstable, and the outer layer of the star is ejected leaving behind the core. This is known as a white dwarf, and it emits radiations which ionise the gas atoms surrounding it; this leads to spectacularly colourful displays known as a planetary nebula. Eleanor, Year 10
When a huge star runs out of gas and reaches the end of its lifetime, it burns through all the gases (hydrogen, helium, neon, silicon, oxygen and carbon) until it reaches iron. The fusion process that creates iron does not create any energy. This means that the star becomes unstable as the radiation is no longer able to halt gravitational collapse. The core collapses into itself when the iron builds up to a certain mass because it can no longer support itself. This creates a supernova as well as a very dense black hole if the star is big enough. The huge amount of mass is concentrated into a very small area which is why they are so dense and their gravitational pull is so powerful. Some black holes are also thought to be created during the big bang. There are three types of black holes: stellar-mass black holes, supermassive black holes and intermediate-mass black holes. Everything near a black hole gets sucked in and stretched to its breaking point, even light, which is why they are black. A black hole doesn’t have a surface, instead it is just emptiness. Black holes are invisible. We know that black holes exist because of how material such as plasmas, stars and dust that surround them are affected. Black holes are usually surrounded by a spirally disc of material that get so hot that they give off x-rays. The first black hole was discovered by John Wheeler, an American astronomer, in 1971. The concept of black holes where first thought of by John Mitchell, a British philosopher and astronomer. He called them “dark stars”. The French mathematician, Pierre-Simon Laplace, also came up with the idea of black holes in 1796. But they were proven to exist later by Einstein’s theory of General Relativity. His theory showed that light does get affected by gravitational pull, which is what happens in black holes. Most galaxies have a few black holes in their centre. Our galaxy has around 100 million and they vary in sizes, the biggest has a mass of 4 million Suns. But that’s not that big considering the biggest black holes that scientists have found in our Universe can hold up to 5000 times more massive. The biggest black hole that scientists have discovered yet is in the constellation Perseus and has a mass of 17 billion Suns. It is known as object S50014+81. There are three measurable properties, called parameters, of a black hole: it's spin, mass and overall charge. These are the only ones that an outside observer is able to know. This idea is called the ‘no hair theorem’ because however ‘hairy’ or complex something that gets sucked into a black hole is, it will get reduced down to its spin, mass and charge. One of the effects a stellar-sized black hole has on nearby objects is called ‘spaghettification’. It is, quite obviously, when an object becomes stretched out and a compression occurs in the centre, until it reaches its limit and rips apart. This happens due to a gravitational gradient. For example, if you were falling feet first into a black hole (highly unlikely), your feet are physically closer to the black hole and therefore have a stronger gravitational pull towards it than your head. This starts to stretch you out further and further. Also, as your arms are not directly in the centre of your body, they will be pulled in a different vector than your feet or head which causes the edge of your body to be brought inwards, creating a compression in the middle. Overall, it’s not good news for you if you are falling feet first into a black hole!
The edge of a black hole is called the ‘event horizon’. Professor Lawrence Krauss, a theoretical physicist, said, ‘We call the event horizon an event horizon quite simply because it separates space into two regions.’ Gravity near a black hole is so strong that it slows down time. Inside a black hole, time stops. ‘You can never observe an object fall all the way through an event horizon,’ Professor Lawrence Krauss said. As an object gets closer to the black hole, it would seem to fall ever more slowly until, just before it falls through completely, it would freeze and stop moving. This is because its clock is moving infinitely more slowly compared to ours. But it would have actually carried on moving and would have fallen through the event horizon into the black hole. Then it, along with everything else that gets sucked into the black hole, would be pulled towards the centre, which is called the singularity. If you were to fall through the event horizon, the horizon splits into two: the horizon and the anti-horizon. You would fall through the horizon and so it says behind you, while the anti-horizon continues to remain ahead of you and you would never fall through it. A German physicist and astronomer, Karl Schwarzschild, found an equation to solve the size of a non-rotating black hole’s event horizon. This was called the Schwarzschild Radius. When black holes reach the end of their life, they evaporate through the ‘Hawking radiation’ process. This is when, at the edge of a black hole, by the event horizon, one of the virtual particles is pulled into the black hole while the other escapes and becomes a real particle. This means that over an extremely long period of time, black holes lose energy. They become very small and evaporate. Black holes do not obey the laws of physics that we know of. Instead they must follow bigger and more complex laws that scientists have not discovered yet. Selina, Year 10 |
Tormead ArticlesA collection of articles from Tormead Students on topics in Astronomy. ArchivesCategories |