The Hubble Catalog of Variables
The Hubble Catalogue of Variables is a three-year project funded by the European Space Agency (ESA), which was recently launched at the National Observatory of Athens, Greece. The goal is to produce a catalogue of variable sources chosen from the 30 million sources in the Hubble Source Catalog (HSC), validate those candidates and make them available in a catalogue.
Over its 25 years of operation, Hubble has visited some regions of the sky multiple times, providing an opportunity to conduct a systematic search for variable objects among the sources in the HSC. The Hubble Catalogue of Variables (HCV) is expected to contain one of the largest collections of variable point sources and extended objects available, spanning a long time baseline up to 25 years, and reaching unprecedented magnitude depths.
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Massive Stars
Massive stars are stars with mass of more than 8 solar masses.
During their short and luminous lifetime, strong photospheric processes yield high mass loss rates. While on main-sequence, they are found as O or early B-type stars whereas at their end-state evolution and up to 25 solar masses, as red, dusty supergiants. Subsequently, they conclude their life as core-collapse supernovae enriching their circumstellar environment with metal-rich material. Owing to their strong mass losses, intermediate massive stars reveal their hydrogen-stripped stellar cores, commonly known as Wolf-Rayet stars. The most massive and thus rarest stars, proceed as Luminous Blue Variables directly after the main-sequence, exhibiting spectacular outbursts.
Supernova/ Transients
Supernovae are often seen in other galaxies. But supernovae are difficult to see in our own Milky Way galaxy because dust blocks our view. In 1604, Johannes Kepler discovered the last observed supernova in the Milky Way. NASA’s Chandra telescope discovered the remains of a more recent supernova. It exploded in the Milky Way more than a hundred years ago. A supernova happens where there is a change in the core, or center, of a star. A change can occur in two different ways, with both resulting in a supernova. The first type of supernova happens in binary star systems. Binary stars are two stars that orbit the same point. One of the stars, a carbon-oxygen white dwarf, steals matter from its companion star. Eventually, the white dwarf accumulates too much matter. Having too much matter causes the star to explode, resulting in a supernova. The second type of supernova occurs at the end of a single star’s lifetime. As the star runs out of nuclear fuel, some of its mass flows into its core. Eventually, the core is so heavy that it cannot withstand its own gravitational force. The core collapses, which results in the giant explosion of a supernova. The sun is a single star, but it does not have enough mass to become a supernova. Scientists also have determined that supernovas play a key role in distributing elements throughout the universe. When the star explodes, it shoots elements and debris into space. Many of the elements we find here on Earth are made in the core of stars. These elements travel on to form new stars, planets and everything else in the universe.