Take a look at these images...
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| Explosion of a Star |
They are simply breathtaking. The more you observe them, the more details you catch, and the more you enjoy the sight of a supernova. Yes, what you are looking at right now is the death of a star. All stars run out of their hydrogen gas fuel and die. How a star dies is largely determined by how much matter it contains. Stars with the mass of our sun expand and become red giants. On the other hand, stars with high mass become red Supergiants.
The supernovae are caused by these supergiants. They destroy themselves in a huge explosion – the supernova - that, as seen from Earth, is colorful and magnificent. But if you were to find yourself close to a supernova, you would probably die. I mean, fair enough because in any case, the death of massive stars can trigger the birth of other stars.
You die, but someone else might be born. In this video, however, we want to understand if there is a minimum safety distance between us and a star that is about to become supernova: a minimum distance that could save us. A supernova is the spectacular explosion of a massive star and these massive stars can be up to several million times the mass of our Sun. Our Sun is not massive enough to trigger a stellar explosion, requiring more massive stars. However, if it ever exploded as a supernova, it probably wouldn’t incinerate the entire Earth.
Instead, the resulting shock wave would extinguish the side of the Earth facing the Sun. Basically, it would be better for you to be sleeping on the night side of the Earth. Everyone would be facing serious problems. For instance, take our sun’s normal surface temperature, about 5778 Kelvin. It’s hot as hell! Well, this temperature would feel like Antarctica to people on Earth. Scientists estimate that the planet as a whole would increase in temperature to roughly 15 times hotter than the normal surface temperature of the Sun.
Basically, you would be roasted. Moreover, when a star explodes as a supernova, material from the star is ejected at high velocities, and this material comes from the star itself. This process is therefore characterized by sudden mass loss. The sudden decrease in the sun’s mass might cause our planet to wander off into space. For sure, we would not be orbiting in the same plane or at the same distance as our star. Clearly, the sun’s distance, which is 8 light-minutes away, isn’t safe at all if it were to explode in a supernova. Fortunately, it won’t. What is the closest safe distance?
What is the Closest Safe Distance?
According to NASA, a supernova needs to be within 50 light-years of Earth before it feels its harmful effects, so we can escape the effects entirely. This is a huge distance, but why 50 and not - say – 30 light-years? Let’s see what would happen if the supernova exploded at this huge distance, but still not enough for us to be safe. This would happen because supernovae are so energetic that they emit X-rays and gamma rays.
These powerful emissions can destroy the ozone layer that protects us from solar ultraviolet rays. These radiations could cause mutations in the earthly life. Also, radiation from a nearby supernova could change our climate. More direct effects would follow. For instance, phytoplankton and reef communities would be particularly affected. Such an event would severely deplete the base of the ocean food chain, which in turn means mass extinction for several species. The good news is, there are no stars within 50 light-years of Earth poised to become a supernova.
It happened at a safe distance, approximately 168,000 light-years away. This is how Hubble observed it from space. This image was taken with Hubble's Wide Field and Planetary Camera 2, back in 1995. It shows the orange-red rings surrounding Supernova 1987A in the Large Magellanic Cloud. Before that, the last supernova visible to the eye was documented by Johannes Kepler in 1604, 418 years ago. It exploded about 20,000 light-years away from us, but it shone more brightly than any star in the night sky. It was even visible in daylight!
As far as we know, it didn’t cause earthly effects. To date, there is still no full consensus in the scientific community on how much each of these channels contributes to the total number of IA supernovae we observe in the universe. But in the case of Kepler's supernova, we tried to understand something more. We tried to reconstruct the identity of the stellar system at the origin of the explosion through chemical and kinetic analyses of the gas and nearby stars.
Scientists concluded it was the result of a merger between two white dwarfs. Amazing. So, we have made sure that no supernova will explode at an unsafe distance from the Earth, so we can keep dreaming our sweetest dreams, for now. We also said that a supernova is a very rare event to witness during your lifetime as well. Is there any chance for our generation to observe one of them? This is much higher than the actual observed rate, implying that a portion of these events has been obscured from Earth by interstellar dust.
The deployment of new instruments that can observe across a wide range of the electromagnetic spectrum, including neutrino detectors, means that the next such event will almost certainly be detected. As for dangerous supernovae, no one really knows. One estimate suggests that a dangerous supernova event could occur around Earth every 15 million years. Another states that, on average, a supernova explosion occurs within 33 light years of Earth every 240 million years. So you see we really don't know. It is something unexpected. Since we're talking about supernovae here, let's learn about some stars that are actually supernova candidates.
Type II supernovae
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| Type II Supernova |
First, you need to know that there are actually two different types of supernovae. There are classic explosions associated with so-called type II supernovae. It has as its progenitor a very massive star of at least eight solar masses near the end of its active lifetime. (They are only seen in spiral galaxies, often near the arms).
Supernova explosions occur when material falls from the outer layers of stars. This material then rebounds from the core, which stops collapsing and suddenly presents a solid surface to the flowing gases. Unlike Type II supernovae, Type I supernovae have a different explosion process, although we are still learning more about how they work.
Type I supernovae can be divided into three subgroups IC, IB and IA on the basis of their spectra. Type Ia supernovae are thought to originate in binary systems consisting of a medium-mass star and a white dwarf, with material from its larger companion streaming into the white dwarf. About 150 light-years from our Sun is a binary system called Ike Pegasi.
It hosts the closest known supernova progenitor candidate. The main star of the system - Ike Pegasi A - is a normal main sequence star, unlike our Sun. A possible type I supernova is another star - Ike Pegasi b. This star is a massive white dwarf. White dwarfs are extremely small and dense, and IK Pegasi B orbits closer to IK Pegasi A than Mercury does to our sun!
How do we expect this to explode??
So how do we expect this explosion to happen? When the A star begins to evolve into a red giant, it is expected to grow to a radius where the white dwarf can accret or absorb material from A's expanding gaseous envelope. When the B star gets big enough, it can collapse in on itself. This will start the show. And our telescope will be delighted to catch it.
Another star that goes supernova every so often is Betelgeuse, one of the brightest stars in our sky, part of the famous constellation Orion. Betelgeuse is a supergiant star, and as such, is intrinsically very bright. Betelgeuse is one of the most famous stars in the sky because it will one day explode and be destroyed, with an interesting fact that it will be so bright that it can be seen directly from Earth with the naked eye. Furthermore, what we know from theory is that if a red supergiant like Betelgeuse dims sharply and becomes a deep red, then a supernova is likely imminent.
What's really interesting is that, even though Betelgeuse is unlikely to explode in our lifetime, we've seen it mysteriously dim. This has fueled speculation that the star may explode. The event will provide a spectacle Earthlings haven't seen in centuries: the last supernova in the Milky Way that could be observed from Earth was in 1604.
The time of day for the week will be visible. What astronomers later found was that the dimming was likely due to more mundane processes, such as a blob of unusually cold material on the star's surface, a dust cloud crossing its line of sight, or perhaps a black hole. One thing is certain: we are not witnessing the sudden explosion of a star. However, there will come a day when Betelgeuse explodes. When this happens, Betelgeuse will shine brightly for weeks or months, perhaps as bright as a full moon and visible in daylight. Don't worry, since it's 430 light-years away from our Sun, life on Earth won't be affected in any way. Hey! This video ends here! Thanks for watching! What do you think about supernova?