#type 1a supernova

JWST Finds Hope

When it comes to calculating the expansion of the universe since the big bang, the Hubble constant has been a source of frustration, simply because different techniques yield different results.

When a team of astronomers looked at a recent JWST image of a gravitationally lensed galaxy, they noticed 3 dots that were not there in the Hubble image of the same object.

Analysing the wavelengths of this light, the team were able to assert that it was a type 1a supernova, from a galaxy 10.3 billion light years from Earth.

Type 1a supernova are common, a white dwarf in a binary system with another star, and if they get too close, it begins to pull material onto it, which increases the mass of the white dwarf until it too collapses causing a supernova.

What's special about this is, these supernova are always the same size, and therefore brightness, which we can used to determine the distance.

Take a few readings, and you can work out how fast the object is moving away from us, and therefore the expansion of the universe.

Most type 1a supernova's are only visible to us in the nearby universe, what the team had found was a type 1a in the old universe, and this could be the key to solving the Hubble tension, the differing results given by nearby objects and far away ones (using different techniques).

SOME SUPERNOVAE NOT SO SUPER Before a white dwarf goes supernova, it goes through a process called gravitationally confined detonation (GCD). This means that an ignition point starts to burn near the dwarf's center and slowly makes its way to the surface the same way an air pocket in a body of water would make its way to the surface. Once this ignition point makes way to the top it propagates across the whole surface of the dwarf until it all collides on the opposite side and triggers a severe detonation. This detonation would in turn completely consume the dwarf and send all its matter flying off into stellar space. When this happens we have what's called a Type Ia supernova. This scenario doesn't always play out however.

(ESA/Hubble)  The background image shows a wide-field view of the night sky as seen with the Palomar Observatory located on Palomar Mountain, California. The leftmost image shows observations made with the Sloan Digital Sky Survey (SDSS). The central image was taken by the NASA/ESA Hubble Space Telescope and shows the lensing galaxy SDSS J210415.89-062024.7. The rightmost image was also taken with Hubble and depicts the four lensed images of the supernova explosion, surrounding the lensing galaxy.

Credit: ESA/Hubble, NASA, Sloan Digital Sky Survey, Palomar Observatory/California Institute of Technology

About the Object Name: iPTF16geu Type: Early Universe : Star : Evolutionary Stage : Supernova

SN 1006

7,200 light years from Earth in the constellation of Lupus, the remains of a Supernova seen from Earth in 1006AD and most likely the brightest ever observed stellar event in recorded history, at around -7.5 magnitude, brighter than the planet Venus.

While the explosion was thought to be outside of the 1 kpc range for potential significant effect on Earth, the outburst can be found in nitrate deposits in Antarctic Ice.

It is thought to have been a type 1A supernova, as no neutron star or black hole has been detected since.

SN 2023ixf

Supernova are incredibly rare, from time to time we spot a distant one, but when we get one in a nearby galaxy or even our own, it's incredibly exciting for astronomers.

The last observed supernova in the Milky Way was in 1604, known as Kepler's supernova, which occurred 20,000 light years from Earth and got as bright as mag -2.5, it would have been the brightest star in the sky by some way (Sirius being -1.3), it is thought there may have been a few more since, but that they failed to become bright enough to the human eye having been concealed by dust and gas. It is thought this was a type 1A supernova.

SN1604 remnants

SN1987A occurred 150,000 light years from Earth but not in our Milky Way, but it's companion galaxy the Large Magellanic Clouds. Unlike SN1604, it was a type 2 supernova, a huge star that had collapsed having built up iron at it's core that it couldn't fuse, and when fusion energy stops pushing outwards, gravity wins ! The star collapsed.

Type 1 supernova come in a variety of flavours and are particularly interesting because they tend (Although not always) to explode with the same light output, allowing us to use these explosions to then predict the actual distance, or what we call Standard Candles in Astronomy.

SN2023ixf was similar to the SN1987a, a type 2 but at 20.87 million light years from Earth, it's close enough for us to observe. Much of those observations, especially in the past, were based on Radio output, and that should be useful in this new supernova, but many type 1a supernova's don't output much in the way of radio waves, and that's because of the way they occur.

Unlike type II. type 1a's occur in a tight binary partnership. One of the stars, maybe similar size to our Sun has died and become a white dwarf. Eventually it's companion also enters it's old age, expands and the white dwarf now starts pulling in huge amounts of hydrogen from the star's atmosphere, and increasing in mass.

Once it hits the Chandrasekhar limit of around 1.4 times the mass of our Sun, the weight of the white dwarf begins a second collapse, and goes supernova as it becomes a neutron star, often ejecting the old companion into space.

This is why many Type 1a supernova have similar brightness, because they explode only when they reach a point of collapse.

Credits for the title images go to @OkanaganAstro on Twitter who posted them when first spotted.

Other sources

Heavy Metal Sub-dwarfs and the Tear Shaped Star

I've often discussed the standard model for main sequence stars beautifully depicted on the Hertzsprung Russell Diagram, but stars don't always obey the rules, and as you'd expect from a "Heavy Metal" star .. these sub-dwarfs certainly don't.

TThe main sequence shows the stars fusing hydrogen in their core (A), eventually when they run out they bloat and become Red Giants (B) or in some cases super giants (C). The super giants will eventually go supernova and leave a neutron star or a black hole (not represented on this scale), but the smaller stars end up as white dwarfs (D).

Hot stars are generally class O or B (blue stars), and as you'll see from the diagram, they are also very luminous and high mass stars, but not all of them are.

In a few very special cases, some hot stars are classed as sub-dwarf, similar to our Sun, but O or B type. These stars are thought to be super giants that have by interaction with a partner binary star, have lost much of their atmosphere and possibly survived a type 1a explosion, effectively the core remnants that managed to escape, or was left behind somehow.

Some of these incredibly peculiar stars have very high amounts of metals. In astronomy Hydrogen and Helium are considered non-metallic, while the rest of the elements are, but heavy metals will constitute elements from Lead upwards in the periodic table, and it is theorised they may have entire layers of such metals within the atmosphere of the stars themselves.

These metals can only have come from other supernova, probably related to the particular nebula they were first born from.

Astronomers at Warwick University have spotted one such hot sub-dwarf interacting with what is thought to be a white dwarf partner. This interaction is drawing mass from the sub dwarf onto the heavier white dwarf. Eventually the mass of the white dwarf will be sufficient to begin collapse and creating a type 1a supernova.

The effect is to create a star shaped like a tear, and the team in Warwick were able to monitor it and detect the odd shape, while not being able to directly see the white dwarf which is far dimmer.

The star is HD265435 and is 1,500 light years away, meaning that if it did go supernova, it would be unlikely to cause any problems here on Earth, but would light up the sky quite dramatically for a few months.

NGC 1365 and a Supernova This beautiful galaxy lies about 56 million light-years away in the constellation Fornax. In 2012, a type 1A supernova was observed in this galaxy, and you can see that explosion in this shot. The intense, blue supernova adds to the charm of this already picturesque galaxy.