The document discusses different types of supernovae and their potential effects on Earth. It describes the Crab Nebula, formed from the remnants of a 1054 supernova, and supernova remnant N 63A in the Large Magellanic Cloud. Type Ia supernovae, which originate from white dwarfs, are considered most dangerous if close enough to affect Earth by depleting the ozone layer through gamma rays. A nearby supernova within 100 light years could impact the biosphere and may have caused a past extinction event.

1. Super Novae Hallmarks

2. SD1994D in the NGC4562 Galaxy

3. Crab nebula Associated with 1054 supernova It is a pulsar wind nebula

4. Crab nebula This composite image shows X-ray (blue) and optical (red) radiation from the Crab Nebula's core region. A pulsar near the center is propelling particles to almost the speed of light. This neutron star is travelling at an estimated 375 km/s.

5. Supernova Remnant Supernova remnant N 63A lies within a clumpy region of gas and dust in the Large Magellanic Cloud

6. Wolf-Rayet star This is expected to cause a supernova in the near future. The nebula around Wolf- Rayet star WR124 is located at a distance of about 21,000 light years . Wolf-Rayet star

7. A near-earth supernova A near-Earth supernova is an explosion resulting from the death of a star that occurs close enough to the Earth (roughly fewer than 100 light-years away) to have noticeable effects on its biosphere . Gamma rays from a supernova induce a chemical reaction in the upper atmosphere , converting molecular nitrogen into nitrogen oxides , depleting the ozone layer enough to expose the surface to harmful solar and cosmic radiation . This has been proposed as the cause of the end Ordovician extinction , which resulted in the death of nearly 60% of the oceanic life on Earth.In 1996, it was theorized that traces of past supernovae might be detectable on Earth in the form of metal isotope signatures in rock strata . Subsequently, iron-60 enrichment has been reported in deep-sea rock of the Pacific Ocean .

8. Type Ia Supernova Type Ia supernovae are thought to be potentially the most dangerous if they occur close enough to the Earth. Because Type Ia supernovae arise from dim, common white dwarf stars, it is likely that a supernova that could affect the Earth will occur unpredictably and take place in a star system that is not well studied. One theory suggests that a Type Ia supernova would have to be closer than a thousand parsecs (3300 light-years) to affect the Earth. The closest known candidate is IK Pegasi (see below). Recent estimates predict that a Type II supernova would have to be closer than eight parsecs (26 light-years) to destroy half of the Earth's ozone layer.

9. Type Ib and Ic Supernovae

10. A near-earth supernova A near-Earth supernova is an explosion resulting from the death of a star that occurs close enough to the Earth (roughly fewer than 100 light-years away) to have noticeable effects on its biosphere . Gamma rays from a supernova induce a chemical reaction in the upper atmosphere , converting molecular nitrogen into nitrogen oxides , depleting the ozone layer enough to expose the surface to harmful solar and cosmic radiation . This has been proposed as the cause of the end Ordovician extinction , which resulted in the death of nearly 60% of the oceanic life on Earth.In 1996, it was theorized that traces of past supernovae might be detectable on Earth in the form of metal isotope signatures in rock strata . Subsequently, iron-60 enrichment has been reported in deep-sea rock of the Pacific Ocean .