Three things that I love to write аbout: beautiful spiral galaxies and exploding star, and astronomical mysteries.
This makes NGC4666 an ideal target. It's definitely spectacular and a star exploded in it. And it's not known why the star's corpse behaved as it did.
NGC 4666 is a similar spiral galaxy to the Milky Way. We see it just a few degrees away from being edge-on so it looks almost like an ellipse. It's an illusion due to perspective. If it were seen face-on, it would probably look almost circular.
It was very close to me, but the distance is not well-known. One source claims it is 48 million light-years away, judging by the brightness of an exploding Star in it. A different paper, however, looked at many different methods and came up with a distance of 55,000,000. We know that distant galaxies are moving away from us due to the expansion. The faster they retreat, the more we see them. This is known as redshift. NGC 4666's Redshift gives me a distance of 72 million light-years to it!
Hubble Space Telescope image of NGC 4666 spiral galaxy. Photo Credit: ESA/Hubble & NASA; Acknowledgement by L. Shatz
The galaxy is in the same area of the sky as the massive Virgo cluster of galaxies. If it's falling into the cluster's combined gravitation, it could skew its redshift. One paper accounting for this gives a distance closer to 85,000,000 light years. It is likely that it is 65 million lightyears away, if we average the different values.
NGC 4666 is known as a starburst galaxies. It is undergoing a mildly intensive episode of starbirth, producing them at a rate between 3-7 times the speed of the Milky Way. Radio waves and Xrays detected this. The powerful winds created by young massive stars interacts with the gas surrounding them, causing it to glow in light that we can't see. There are visible light filaments (or optical) that can be seen in light emitted from warm hydrogen. I swear, the Hubble image above shows the darker tendrils sticking out perpendicular to the galaxy's disc. Although they might look illegible, I will admit that I noticed them looking this way before I realized the galaxy was creating this superwind for newborn stars.
Hubble did not observe this galaxy because of its exploding star. It was actually because it was the home to an exploding supernova. When you think about those, you might imagine a huge star like Betelgeuse near the end of its lifespan. This is called a Type II supernova or a core collapse.
Artist's drawing showing the RS Ophiuchi star system. This is a symbiotic star that orbits a recurring nova and where a white dwarf accumulates matter from the star around it. Credit: David Hardy & PPARC Photo: David Hardy & PPARC
This was a Type I explosion, which is when a white dwarf explodes. These are the remnants of smaller stars, such as the Sun, after they have run out of nuclear energy. The star expands to a red giant and blows away its outer layers. This exposes the hot, dense core of the star to space, a white dwarf. The intense gravity of the white dwarf could steal material from other stars, which would cause the star to pile up on its surface. If the conditions are right, it can be squeezed so hard that the pilfered hydrogen undergoes thermonuclear fission, which could disrupt the entire star. It is also possible that it orbits another white dwarf. They eventually spiral together and collide. It could happen either way: KABOOM! Supernova.
It is expected that the expanding debris will undergo a complex atomic process approximately 500 days after the supernova explosion. This causes the visible light it emits suddenly to drop, and the infrared makes it brighter. This is difficult to see because supernovae are often far away and get dimmed by time.
Happily, however, a Type Ia was found in NGC 4666 in December 2014. It was called ASASSN-14lp because it was the first time it was seen by the All-Sky Automated Survey for Supernovae. Although it was very bright for its type, it was otherwise quite normal. It's a good thing, though: Being so close in galactic terms and being bright made it easier for late-night viewing. Hubble saw the supernova and the galaxy around 860 days after the event.
NGC 4666 is a spiral galaxy with the exact location of Type Ia supernova ASASSN-14lp (the very small blue dot) shown. Photo credit: ESA/Hubble & NASA; Acknowledgement by L. Shatz
ASASSN-14lp decided not to follow the rules. The optical light did not drop rapidly, but it was also lingering. With the light it gave off decreasing slowly with time, observations revealed this. This phenomenon has been observed in a few other supernovae, but it is not known why. All sorts of elements are created by the explosion, including radioactive elements that decompose and release energy into surrounding material. A slowly decaying one could give the expanding debris enough energy so it stays brighter for longer. The debris may change, allowing it to absorb more energy from decay, thereby enabling it to stay brighter longer.
The observations can't tell what is happening or if there is something else going on. It is impossible to find the cause of a supernova by looking at all of them.
It was still emitted light at a speed that made ASASSN-14lp 100,000 times brighter that the Sun, three years later. Supernovae can be fierce.
These Type Ia supernovae can also be used to help understand why the Universal expansion accelerates. These supernovae are very useful astronomically.
Also, supernovae such as this can send out many elements like calcium and iron into space. They can also hit gas clouds. These clouds eventually collapsed to form stars or planets, which happened approximately 4.6 billion years ago. You are.
Supernovae are responsible for our existence, and it is possible to predict the future of the Universe from them.
It's not bad. It's a beautiful galaxy, an exploding Star, and an astronomical mystery. Plus, the wonder and awe that we receive when we look at the cosmos around. It's a sweet deal to observe NGC 4666.