Novae

Novas are cataclysmic stellar events that fall into two categories: “Classical Novae” and “Supernovae”.

Classical Novae eruptions are the result of a close binary system, usually consisting of a Main Sequence or Red Giant primary star and a white dwarf secondary. If the stars are in close proximity matter will flow from the primary onto the secondary up to the point where a rapid runaway thermonuclear fusion reaction ensues which expels the accreted matter into space along with a significant explosive flash.  The secondary is not necessarily destroyed and the process may recur over time.

Supernovae on the other hand is the end stage gravitational core collapse of a massive star which results in the cataclysmic destruction of the star and a many millions fold increase in luminosity.

Observing and recording the rapid rise and then decline in brightness of these unpredictable transient stars is of interest to both professional and amateur astronomers since they can tell us a lot about the distance, mass, and chemical composition of the stars themselves and the galaxies or clusters of which they are a part.

The Crab Nebula also known as Messier 1, is the quintessential example of a Supernova. This supernova remnant is located in the constellation of Taurus and is 6,700 light Years distant and 11 LY in diameter. When the star underwent its final stage gravitational collapse, the resulting thermonuclear detonation was bright enough to be seen in broad daylight. How do we know this? It was chronicled by Chinese Astronomers back in the year 1054 AD. In the center of the Nebula is the remnant of the progenitor star – now called a Neutron Star – has collapsed down to a diameter of about 20 miles but with a mass 1.4 times that of our Sun. A teaspoon full of matter from this star would weigh a billion tons !
This recent Classical Nova discovered on March 18, 2021, was located just 24 arc-minutes south of the star cluster M52 in the constellation of Cassiopeia. Since its discovery it brightened from a dim 15.6 magnitude star to naked-eye visibility at magnitude 5.3 – an over 10,000 fold increase in brightness. It has since faded back to its quiescent brightness of ~12.5 magnitude.
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The above photo shows the Galactic Supernova SN 2020uxz in the constellation of Pisces near its peak brightness of magnitude 13.5. The supernova is a member of the the faint Galaxy NGC 514 located 83 million lightyears away. The brightness of the supernova is many times that of the NGC514 as a whole which is only faintly visible, while the other stars in the frame are foreground stars and members of our own “Milky Way” galaxy.
Thirteen weeks later, SN 2020uxz has faded to magnitude 16.5 – the same brightness as the nearby field star located directly above it in the photo. In this 20 minute photograph the details of its faint host galaxy are more clearly defined. Even at this late date, the brightness of this single star rivals that of the central core of NGC 514.
The light-curve above shows how the brightness of SN 2020uxz has changed since its discovery in early October 2020 to January 2020. My own measures of its brightness over this time period are shown as the brown clover-shapes on the plot. It will soon fade from view becoming indistinguishable from the trillions of other stars that make up NGC514.
Another faint visitor making a transient appearance in the summer sky of 2020 was “Nova Cassiopeia 2020”. Classical Novae are the result of a close binary star system where there is a transfer of mass between the stars which leads to instability and a thermonuclear explosion which rapidly increases the brightness of the star perhaps by as much as 10 to 20 magnitudes over the course of several days. But just as quickly the star will soon begin to fade back to its original state. By the time of my photo above -taken two days past its maximum – it had already dimmed to mag 11.3 from its peak of 10.6 .
By Mid December N Cas 2020 had faded from view
The light-curve for N Cas 2020 is much more complex than that for SN 2020uxz, with numerous fluctuations in magnitude before fading completely from view. This is an indication of more complex atomic interactions after the initial detonation. My own measures of its brightness over this time period are noted by the brown clover-shapes on the plot.
Supernova SN2017ein is an example of an extragalactic supernova. The extraordinary explosive brightness of this single star stands out prominently from the billions of other stars in the Galaxy NGC 3938.
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The brightness of supernova ASASSN141p rivals that of the entire galactic core of NGC 4666.
Supernova 2017eaw is so bright that it appears to be one of the many foreground stars in our own galaxy but it is actually located in one of the faint  spiral arms of the galaxy NGC 6946.  Its brightness rivals that of the core of NGC 6946 itself.
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A classical nova visible in the Andromeda Galaxy. The inset photo on the right shows the nova just 4 days after its discovery (Dec 31, 2018).
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Supernova SN 2022hrs is located in the spiral galaxy NGC4647 in the constellation of Virgo. Nearby is the elliptical galaxy messier 60 (M60) and the faint Ultra-Comact Dwarf Galaxy UCD-1. UCD-1 which barely shows in my photo may be the densest galaxy known, with a stellar density of over 100 stars per cubic light year and a 20 million solar-mass black hole lying at its center.