4. Why do star twinkle?
They don’t. Their light gets distorted by churning gases in Earth’s atmosphere – hence why telescopes are constructed on mountains, above the bulk of the air. We only notice the twinkling as stars are tiny points of light; planets don’t twinkle as they’re close sufficient to appear as tiny discs.
5. Which is the farthest star that we can see?
Ignoring occasional flare-ups such as supernovas, the farthest star we can reliably see with the naked eye is the obscure V762 Cassiopeiae, which is just observable under dark skies and is about 16,300 light years away. The most distant well-known star, meanwhile, is Deneb, the brightest star in the constellation of Cygnus, the Swan. It lies a still inspiring 2,600 light years away and is the 19th brightest star in the sky, proposing it is about 200,000 times more luminous than the Sun.
6. What is neutron star?
Neutron stars are extreme stellar remnants made after a giant star goes supernova. When the star runs out of fuel, it breakdowns under its own weight, generating a huge shockwave that compresses the core from the size of our Sun to approximately the size of London. Atomic nuclei in the core are torn into their subatomic components and protons are transmuted into yet more neutrons that can reach crazy densities: a pinhead of neutron star material can weigh as much as a fully laden supertanker!
7. How are stars named?
The brightest stars have proper names that often originated with Ancient Greek or Arabic astrophysicists – for instance, Sirius, the brightest star in the night sky, has a name derived from the Greek for ‘scorcher’. The bright stars in each constellation are also named with Greek letters in alphabetical order – so Sirius is also Alpha Canis Majoris.
8. Can we tell if the stars we see have died?
Stars take millions or billions of years to move through their life cycles, but the light from stars in our galaxy generally spends a few thousand years at most travelling to Earth. On the law of averages, then, it’s pretty unlikely that a star will have died in the intervening time, but there are some exceptions, eg Eta Carinae might have already exploded.
9. How can a star burn with no oxygen in space?
Blame astrophysicists for the misleading word ‘burn’ – stars aren’t going through the same kind of combustion we see on Earth. As an alternative, stars feed off their hydrogen fuel by forcing individual nuclei together until they transmute into helium and ultimately other elements in a process known as nuclear fusion.
10. What exactly is a white dwarf?
White dwarfs are the superhot, burnt-out cores of stars like the Sun, exposed when a dying red giant star sheds its outer layers. With no nuclear fusion left to support it, the core collapses under its own weight until it is about the size of Earth, but normally still has approximately half a Sun’s mass of material.
12. What’s the difference between a nova, supernova and hypernova?
Novas are comparatively small explosions in double star systems. They come about when a white dwarf’s intense gravity tugs material away from a companion star. Gas piles up around the white dwarf and ultimately becomes dense enough to ignite in a burst of nuclear fusion. Most supernovas, in the meantime, mark the deaths of massive stars and the formation of neutron stars. They are triggered when a shockwave tears through the outer layers of a dying star, igniting a firestorm of nuclear fusion. Finally, hypernovas are ultra-energetic supernovas marking the birth of black holes and linked with the release of intense gamma-ray bursts.
13. Which stars are the biggest and smallest?
The largest known star is an unstable red hypergiant called NML Cygni, about 5,500 light years from Earth – its diameter of about 1,600 Suns makes it close to twice the size of Betelgeuse. The smallest star is OGLE-TR-122b, a tiny red dwarf only somewhat bigger than Jupiter and with just a tenth the mass of the Sun. Anything smaller is a brown dwarf.
14. Where is Betelgeuse?
With a diameter large enough to swallow up Jupiter’s orbit around the Sun, Betelgeuse is the nearest supergiant star to Earth 640 light years away in the Orion constellation. Nearing the end of its life, it has developed a series of internal shells producing energy from the fusion of various elements, increasing its energy output to the equivalent of 120,000 Suns. The pressure of radiation pouring out from the star’s interior has caused its outer layers to balloon to a vast size and cool to a deep red.
15. How are stars made?
The birth and death of a star depend on its mass. Average stars like the Sun may live for billions of years and end their lives as white dwarfs, while heavyweights live fast and die young. Ultimately, all star scatter material across space to produce the next generation.
16. How do black holes form?
When a giant star consumes all of the hydrogen fuel for fusion in its core, the fusion process moves out into a spherical ‘shell’ while the core starts to fuse helium into heavier elements. As each fuel source in the core is spent a new shell is made, while the core moves on to fusion of ever heavier elements. Stars with eight times the Sun’s mass continue the process until their cores start to fill with iron. The star cannot produce energy by fusion of iron, so when it tries, its energy supply cuts out and it collapses. The core is squashed to an incredible density, while a shockwave rebounds through the rest of the star, ripping it apart.
In most cases, the star’s core stabilizes as a neutron star, but if the core weighs more than three to four Suns, the pressure between neutrons can’t halt the collapse. The neutrons are torn apart and the core collapses to a single superdense point: a singularity. The singularity’s gravity is so powerful that anything that comes too close – even light – can’t escape from it. As it takes material in from its vicinity, it may briefly release a burst of highly energetic gamma rays along its axis of rotation.
17. How many stars are there in the universe?
Brace yourself for some big numbers. Astrophysicists believe there are possibly somewhere between 10 sextillion (21 zeros) and 1 septillion (24 zeros) stars in total. That’s based on recent findings that there are a lot more tiny, faint stars lurking in large galaxies than formerly believed, and some educated guesswork on the total number of galaxies themselves.
18. If we poured a giant bucket of water on a star, could we extinguish it?
Funnily enough, it would possibly have the opposite effect. The ferocity of nuclear fusion in a star depends on the temperature and pressure in its core, so if we added a huge amount of extra mass to the star in the form of all that hydrogen and oxygen, we’d rise the star’s mass and central pressure, in turn making it shine brighter.
19. How do people use the stars to navigate?
Because objects in the sky stay fixed, even as Earth rotates beneath them, they form a perfect reference point for navigators. If you have an almanac and a precise clock, you can compute your latitude by measuring the height of a star passing across the meridian (north-south line across the sky). Likewise, you can work out latitude by comparing ‘local noon’, when the Sun crosses a particular meridian, with the time at a fixed location such as the Greenwich Meridian.
20. How is the distance to a star calculated?
The only way to measure a star’s distance directly uses parallax – measuring the tiny difference in a star’s seeming position in the sky when we look at it from different points of view (on opposite sides of Earth’s orbit around the Sun). This only works for close stars, but, using parallax, astrophysicists can discover patterns in stellar behavior from which they can work out the brightness of stars independently. They can then use this to extrapolate the distance of more remote stars.