An article published in the “Astrophysical Journal Letters” describes a study on the supernova Sn 2012au. Sometimes supernovae remain bright for a long time if the remnants of the explosion collide with hydrogen layers, but Dan Milisavljevic of Purdue University wondered if this could happen without any interaction of that kind. His team studied Sn 2012au concluding that after the supernova a neutron star of the pulsar type was formed with a rotation and a magnetic field sufficient to create a cloud of gas around it, called in jargon a pulsar wind nebula.
Sn 2012au was identified as a type Ib supernova, which means that it occurred as a result of the collapse of the core of a very massive star that lost most if not completely its outer hydrogen layers. It wasn’t bright enough to be classified as a superluminous supernova but it showed it had a lot of energy and a long duration, becoming the object of various researches to understand the mechanisms behind those characteristics.
The supernova Sn 2012au was detected in the galaxy NGC 4790 in 2012 and is still bright. The image (NASA, ESA, and J. DePasquale [STScI]) shows the galaxy NGC 4790 and in the insets two details that show the area in which the supernova Sn 2012au was seen at the top in 2001 and at the bottom in 2013. These are observations made using the Hubble Space Telescope.
Generally, long-lasting supernovae are related to the presence of hydrogen that formed the progenitor star’s outer layers ejected before the explosion, but in this case the spectral analyzes don’t indicate its presence. When a neutron star is formed after a supernova, in some cases it can accelerate nearby charged particles by creating a cloud of gas around it that can illuminate the materials ejected by the explosion, the pulsar wind nebula.
Dan Milisavljevic predicts that an examination of other very bright supernovae could reveal similar processes. A neutron star that is formed from the remnants of an exploded star may be of the pulsar or magnetar type. It can push outward accelerating the gas so careful measurements made after a few years may show traces of oxygen-rich gases that are moving away even more quickly.
Supernovae are catastrophic events that can be difficult to study when they occur in other galaxies, millions if not billions of light years away, and are only visible because they’re extremely bright for a while. More and more sophisticated instruments are offeringan increasing amount of information about supernovae and astronomers are looking for them carefully to study them together with their possible consequences.
Many elements, including some essential for life on Earth such as oxygen, iron and calcium, are formed in supernovae. The very bright and superluminous ones could emit gravitational waves and could be connected to some types of gamma-ray bursts and also fast radio bursts.
For these reasons, according to Dan Milisavljevic, it’s crucial for us, as citizens of the universe, to understand this type of process. He pointed out that this is a fundamental process in the universe and indeed supernovae have an enormous influence on the surrounding interstellar environment so getting to know the mechanisms of the various types of supernova means understanding why the universe today is as we see it.
