NEUTRON STAR

When a star – larger than the sun – has used up all ‘fuel’ preventing atomic nuclei in its center from fusing, it will collapse under the burden of its own weight. It then explodes as a supernova – and gravity will put the atoms in its center under such a tremendous pressure that electrons and protons come together and become neutrons. The center of the star is transformed – into a gigantic nucleus of an atom made up solely of neutrons - measuring roughly 20 kilometer in diameter, about the size of Metropolitan Copenhagen, but with a mass slightly exceeding that of the suns. This makes a neutron star so incredibly dense that just one teaspoon of neutron star-matter would equal Mount Everest in terms of weight.

BLACK HOLES

When collapsing, the biggest stars do, however, not leave behind neutron stars. They leave black holes in stead – which is the result of the concentration of mass in the center of these stars being so significant that the collapse of matter is total. This in turn creates a zone where gravity is so strong, so pronounced, that not even light can escape.

Formation of black holes can also take place when neutron stars collide – and gigantic black holes can be found in the center of galaxies.

KILONOVA

A kilonova - a.k.a. macronova - is the result of a collision between two neutron stars. This event sets free vast quantities of matter – emitting a very bright light, in particular due to the decay of heavy elements.

The light from a kilonova will be far stronger than that from a nova – but not near as bright as the light emitted from a supernova.

NOVA

A nova is a temporary recrudescence of an otherwise extinct star. When an extinct star belonging to the white dwarf-class is part of a binary star system, it may attract gas from the other star in this system - thus causing a concentration of hydrogen on its own surface. This hydrogen may explode like a colossal bomb which will make the white dwarf suddenly light up and be far brighter than what is usually the case; a state which may continue for weeks, sometimes for months.

SUPERNOVA

The biggest stars perish in mega supernova-explosions – which, for a short period, can make them light up with an effect surpassing that of all stars in a galaxy combined. Supernovas can also form in binary star systems where matter is being exchanged between the stars. When a supernova perishes, it leaves behind either a neutron star or a black hole.

LIGHT YEAR

The distance which light can travel in a year – this equals 9.46 trillion kilometer.

GRAVITATIONAL WAVES

When two objects change direction and/or speed relative to each other, spacetime surrounding them, too, will change – causing emission of gravitational waves: i.e. minor ripples in spacetime. This is e.g. happening when celestial bodies circle each other – and the greater the acceleration, the masses and the density, the stronger the gravitational waves. It is possible to describe gravitational waves as gravity detached from its source and origin, racing through space at the speed of light. Where these waves go, spacetime is slightly altered – which makes it possible to register the strongest category gravitational waves by means of detectors.

GRAVITATIONAL WAVE DETECTORS

In order to detect gravitational waves originating from dramatic events in the universe, extremely sensitive detectors are needed. When a gravitational wave hits, spacetime encounters certain changes. This, initially, will make everything ‘longer on one side and shorter on the other side’ – which, subsequently, will be repeated, this time just vice-versa. The changes occurring are, however, minute – and globally just three scientific facilities have the necessary equipment capable of detecting gravitational waves: The two US-based LIGO-detectors and the Italian Virgo-detector. Gravitational waves are registered and measured by means of laser interferometry – a technology involving to and fro-transmission of powerful laser beams through two perpendicularly placed, kilometer long ‘tubes’. A significant gravitational wave will shorten one of the ‘tubes’ and make the other longer, which can be measured – even though the difference in length equals less than 1/1000 of the size of nucleus of an atom.

ELECTROMAGNETIC RADIATION

With the exception of black holes celestial bodies emit electromagnetic radiation representing a variety of wave lengths. Astronomers are eager to register as much radiation as possible when they examine a celestial body.

GAMMA RADIATION

This is the most energy-rich form of electromagnetic radiation. It is emitted in so called glimpses – representing some of the most dramatic events in the universe. Gamma radiation has, however, difficulties passing through the atmosphere – which is why space telescopes are needed in order to register gamma rays from cosmic sources.

X-RAYS

Like gamma radiation space telescopes are needed to register X-rays. Powerful X-rays may e.g. originate from matter which is about to ‘disappear’ into a black hole.

ULTRAVIOLET RADIATION

Ultraviolet radiation has shorter wave lengths than light we can see and register with our eyes. The sun emits ultraviolet light, but the major part is being held back by the ozone layer. The best way to ‘catch’ ultraviolet radiation is by using a space telescope.

OPTICAL LIGHT

Optical light is the light we can see with our eyes. Light from celestial bodies can be registered by optical telescopes – based on our planet or in space.

INFRARED RADIATION

Infrared radiation has longer wave lengths than visible light. Infrared radiation has problems passing through the atmosphere – however, it can be observed via telescopes situated in locations well above sea level and from air planes and space telescopes. Near-infrared light is the type of light which is closest to optical light.

RADIO WAVES

Radio waves are electromagnetic waves – the waves with the longest wave lengths. They are used for radio transmissions, hence their name, but they are also emitted naturally from many celestial bodies .