“British astronomers have announced the discovery of a supernova in
galaxy M101, which they claim is the nearest supernova of its type for
more than 40 years. The object was discovered at magnitude 17, but
it appears to be rising in brightness, and the team says that it could
become as bright as magnitude 10 within the next few days. That
would bring it well within the reach of small telescopes and even
large binoculars. Amateur astronomers with suitable instruments
should already be able to photograph the supernova, which has the
name PTF11kly. Its position is RA 14:03:05.81, Dec +54:16:25.4.
M101 is currently well placed for observation; it is in Ursa Major,
not far from the well-known stars Mizar and Alkaid/Benetnasch in the
Plough.The supernova was first seen on August 24 at around 8 pm BST,
within the spiral arms of M101. An image taken the previous night
had shown no such object in that position. The discovery was made
from Palomar with the 48-inch Schmidt telescope, which is now operated
robotically by a team of British and American astronomers known as
the Palomar Transient Factory. The object’s spectrum shows that it
appears to be a Type 1a supernova, which occurs when a white-dwarf
star in a binary system explodes.
Supernova M101To find distances in space, astronomers use objects called “standard candles.” Standard candles are objects that give a certain, known amount of light. Because astronomers know how bright these objects truly are, they can measure their distance from us by analyzing how dim they appear. For example, say you’re standing on a street evenly lined with lampposts. According to a formula known as the inverse square law, the second streetlamp will look one-fourth as bright as the first streetlamp, and the third streetlamp will look one-ninth as bright as the first streetlamp, and so on. By judging the dimness of their light, you can easily guess how far away the streetlamps are as they stretch into the distance. For short distances in space — within our galaxy or within our local group of nearby galaxies — astronomers use a type of star called a Cepheid variable as a standard candle. These young stars pulse with a brightness that tightly relates to the time between pulses. By observing the way the star pulses, astronomers can calculate its actual brightnessBut beyond the local group of galaxies, telescopes can’t make out individual stars. They can only discern large groups of stars. To measure distances to far-flung galaxies, therefore, astronomers need to find incredibly bright objects. So astronomers turn to exploding stars, called supernovae. Supernovae, which occur within a galaxy about every 100 years, are among the brightest events in the sky. When a star explodes, it releases so much energy that it can briefly outshine all the stars in its galaxy. In fact, we can sometimes see a supernova occur even if we can’t see its home galaxy. To determine distances, astronomers use a certain type of exploding star called a Type Ia supernova. Type Ia supernovae occur in a binary system — two stars orbiting one another. One of the stars in the system must be a white dwarf star, the dense, carbon remains of a star that was about the size of our Sun. The other can be a giant star or even a smaller white dwarf. White dwarf stars are one of the densest forms of matter, second only to neutron stars and black holes. Just a teaspoon of matter from a white dwarf would weigh five tons. Because white dwarf stars are so dense, their gravity is particularly intense. The white dwarf will begin to pull material off its companion star, adding that matter to itself. When the white dwarf reaches 1.4 solar masses, or about 40 percent more massive than our Sun, a nuclear chain reaction occurs, causing the white dwarf to explode. The resulting light is 5 billion times brighter than the Sun. Because the chain reaction always happens in the same way, and at the same mass, the brightness of these Type Ia supernovae are also always the same. The explosion point is known as the Chandrasekhar limit, after Subrahmanyan Chandrasekhar, the astronomer who discovered it. To find the distance to the galaxy that contains the supernova, scientists just have to compare how bright they know the explosion should be with how bright the explosion appears. Using the inverse square law, they can compute the distance to the supernova and thus to the supernova’s home galaxy.
UPDATE: Supernova in Messier 101 brightens Could be Binocular target in 1 week!
See The Bad Astronomer’s Blog Update !