Supernova is the result of the explosion of a star.
The cover image shows Tycho’s Supernova Remnant as seen in X-ray light from the Chandra X-ray Observatory, in 2008
The supernova that amazed Tycho Brahe
In november 1572, a very bright star appeared in the constellation Cassiopeia.
Cassiopeia is depicted as a queen sitting on a throne, sometimes holding a mirror or palm frond.
The star began as a small, barely visible light, it grew rapidly in intensity until it became a luminary that outshined the rest of the stars in its constellation, brighter than Venus and clearly observable in broad daylight.
Tycho Brahe was able to observe her and tried to calculate with his instruments the distance, which he found infinite, which was beyond his measurement possibilities.
We now know that this supernova exploded 7,500 light years from Earth; the flash from the explosion took that long to reach our planet.
This means that when Tycho Brahe and everyone else saw the birth of this star, it had already been 7,500 years since it had occurred.
There is documentary evidence that in the same year, 1572, Chinese and Korean astronomers were surprised to find a new star in the Constellation of Cassiopeia.
At the site of the SN 1572 supernova, a gigantic gas nebula can be seen today, expanding at several thousand kilometers per second.
This gas, which is still several million degrees, is also an intense X-ray emitting source.
When a star collapses
The evolution of a star depends on its mass. Stars continually lose mass and in the last phases of their lives they lose it much more intensely and can end up with a final mass much lower than the original one.
When the mass decreases to a certain level and the star does not fuse material, it will go into a degenerative process that will cause it to collapse on itself due to gravity.
Depending on its mass, the star can become a white dwarf, a neutron star, a black hole or explode and transform into a supernova.
If the collapsed mass were greater than 200 solar masses, the pressure of the core fusion would cause the star to explode violently.
The balance between both forces makes the stars that we see in the sky are as we know them.
The star will die when the hydrogen in its core is depleted, which will make gravity no longer have anything to prevent the collapse of the star.
It was what we know today as the explosion of a supernova, a cataclysmic event that occurs when a white dwarf begins to grow, until its mass becomes 1.44 times the mass of the Sun.
Supernova NGC 2440
The star NGC 2440, created by a star similar to the Sun in the last stages of its life.
It has expelled its outer layers which now form a cocoon around the stellar core. The material glows due to the ultraviolet light coming from the star.
The white point near the center is a white dwarf and was the core of the star.
At that time, it occurs an internal explosion that throws the material of the star in all directions at immense speeds.
In the image, you can see the location of the shock wave from the explosion as a blue sphere of electrons.
The dust synthesized after the explosion, and the dust that already existed and that has been heated by the event, radiate at a wavelength of 24 microns (represented in red).
The stars in the background and ahead are white.
Novae and Supernovae
These phenomena were initially called stellae novae, “new stars” or simply novae.
Over time, the less luminous ones continued to be called novas, while the more luminous ones were added the prefix “super”.
The emergence of supernovae produces extremely intense flashes of light that can last from several weeks to several months.
They are characterized by a rapid increase in intensity until reaching a maximum, to then decrease in brightness more or less smoothly until disappearing completely.
Supernova discoveries are reported to the International Astronomical Union, which distributes a circular with the newly assigned name.
The name is formed by the year of discovery and the one or two letter designation. The first 26 supernovae of the year have letters from A to Z (eg Supernova 1987A); the following lead to aa, ab, etc.
Supernovae seen from Earth in historical times
The dates indicate when they were observed. In reality, the explosions occurred much earlier, as it took hundreds or thousands of years for their light to reach Earth.
- Year 185 – SN 185 – references in China. Analysis of X-ray data from the Chandra observatory suggests that the remnants of supernova RCW 86 correspond to this historic event.
- Year 1006 – SN 1006 – Very bright supernova; references found in Egypt, Iraq, Italy, Switzerland, China, Japan, France and Syria.
- Year 1054 – SN 1054 – It was the one that originated the current Crab Nebula, it is referred to by Chinese astronomers.
- Year 1181 – SN 1181 – Chinese and Japanese astronomers report it. The supernova exploded in Cassiopeia, leaving the neutron star 3C 58 as a remnant.
Classification of supernovae
The classification of supernovae is based on grouping them according to the absorption lines of different chemical elements that appear in their spectra.
The first key to division is the presence or absence of hydrogen.
If the spectrum of a supernova does not contain a hydrogen line it is classi reported as type I; otherwise, if it contains a hydrogen line, it is classified as type II.
Within these two main groups there are also subdivisions according to the presence of lines corresponding to other chemical elements, such as silicon and helium.
There are type I supernovae that lack helium and instead have a silicon line in the spectrum. They are the most powerful and, sometimes, their brightness is several times higher than that of the galaxy where they are born.
The most accepted theory regarding this type of supernovae suggests that they are generated in a binary system consisting of a white dwarf and a red giant.
The carbon-oxygen white dwarf absorbs its companion star, the red giant, which has an outer envelope basically composed of hydrogen and helium.
The collapse of a dwarf star
The dwarf star adds much of the mass of the red giant to its mass.
When the mass of the white dwarf reaches the Chandrasekhar limit (1.44 times the mass of the Sun), the increase in internal pressure produced by the increase in gravity triggers the collapse of the star, the interior temperatures skyrocket until it starts the fusion of carbon at its core.
This ignition begins in the center and spreads rapidly through the entire volume of the star to its outer layers.
The amount of carbon that burns during the explosion in a few seconds is comparable to that burned in a normal star for centuries.
The enormous energy released produces a powerful shock wave that destroys the star, expelling all its mass at speeds of around 10,000 km / sec and causing an extreme increase in luminosity.
Remants after explosión of a dwar star
Usually there are no traces of the star that caused the cataclysm, but only remnants of superheated gas and dust, which are rapidly expanding away.
If the neighboring star manages to survive the detonation, by not being subjected to the attractive force of the destroyed star, it experiences a change in its trajectory and goes off in the direction it was following at the time of the explosion.
These runaway stars can be detected as they acquire speeds much greater than their surroundings.
This image show the remnant of Kepler’s supernova, the famous explosion that was discovered by Johannes Kepler in 1604.
The red, green and blue colors show low, intermediate and high energy X-rays observed with NASA’s Chandra X-ray Observatory, and the star field is from the Digitized Sky Survey.
This was a thermonuclear explosion of a white dwarf star. These supernovas are important cosmic distance markers for tracking the accelerated expansion of the Universe.
There may also be a supernova generated by the merger of two white dwarfs of the same binary system that together can exceed the Chandrasekhar mass.
This is because two rotating white dwarfs emit gravitational waves and, over time, their orbits approach and accelerate, which in turn accelerates the emission of waves and feeds back the process.
There may come a time when one of the two dwarfs (the less massive), disintegrates and forms a torus (body shaped similar to a donut) around the other star. Then the disc material begins to fall to the surface.
Some notable supernovae
1604 – SN 1604 – Supernova in Ophiuchus, observed by Johannes Kepler; it is the last supernova discovered in the Milky Way.
Galileo used the supernova SN 1604 as proof against the prevailing belief at the time that the sky was immutable.
1885 – SN 1805 – Andromeda supernova, in the Andromeda Galaxy, discovered by Ernst Hartwig.
1987 – Supernova 1987A – outside the Tarantula Nebula, in the Large Magellanic Cloud.
It could be observed a few hours after its appearance, on February 23, 1987. (It is 168,000 light years from Earth).
It was the first opportunity to test, through direct observations, modern theories about the formation of supernovae.
Cassiopeia A – Supernova in Cassiopeia, not observed at the time of its appearance, but estimated to have happened about 300 years ago. It is the brightest remnant in the radio band. It is 11,000 light years away.
2005 – SN 2005ap – This type II supernova is by far the brightest ever observed. It became up to eight times brighter than the Milky Way. This makes it outperform SN 2006gy almost twice.
2006 – NASA reported that the Chandra Observatory (X-ray) had recorded an extraordinarily large and bright stellar explosion, the brightest detected to date.
It is located in the core of the galaxy NGC 1260 and about 240 million light years from Earth. It was named SN 2006gy.
SN 2006gy is the second largest supernova that has been observed to date, five times more luminous than previously observed supernovae, its brightness was 50,000 million times that of the Sun.
It originated from the explosion of a star with 150 solar masses. The director of Chandra observations at the University of California said the data collected so far “gives strong evidence that SN 2006gy was, indeed, the death of an extremely large star.“
Astronomers keep looking for supernovae
In 2006, astronomers discovered another 500 supernovae.
With regard to the data collected by large telescopes, it should be noted that astronomers try to obtain information from them by examining the spectrum of radiation emitted by supernovae.
There are millions of data that are being received from these observatories. Its composition, classification and study make professional astronomers, of various specialties, more than busy during long hours of hard work.
Do not believe that these people are comfortably sitting and looking at the stars. 99.99% of their work is not looking at the sky, but at papers and computer screens.
Tens of thousands of amateur astronomers are freed from this extremely hard work and can devote themselves more freely to fruitful observation.