Aside

How supernovae became the basis of observational cosmology

Supernova classification

Supernova classification

Maria Victorovna Pruzhinskaya, Sergey Mikhailovich Lisakov
This paper is dedicated to the discovery of one of the most important relationships in supernova cosmology – the relation between the peak luminosity of Type Ia supernovae and their luminosity decline rate after maximum light.
The history of this relationship is quite long and interesting. The relationship was independently discovered by the American statistician and astronomer Bert Woodard Rust and the Soviet astronomer Yury Pavlovich Pskovskii in the 1970s.
Using a limited sample of Type I supernovae they were able to show that the brighter the supernova is, the slower its luminosity declines after maximum.
Only with the appearance of CCD cameras could Mark Phillips re-inspect this relationship on a new level of accuracy using a better sample of supernovae. His investigations confirmed the idea proposed earlier by Rust and Pskovskii.
Read more at https://arxiv.org/ftp/arxiv/papers/1608/1608.04192.pdf

KIC 8462852 Faded Throughout the Kepler Mission

Over the four years that the Kepler telescope monitored this mysterious star, its light levels dropped by a total of about 3 percent--but not all at a constant rate. (For reference, the huge dip at the 800 mark is one of the huge dips that originally tipped off scientists that this was a freakin' weird star. "It was off the charts," says Montet.)

Over the four years that the Kepler telescope monitored this mysterious star, its light levels dropped by a total of about 3 percent–but not all at a constant rate. (For reference, the huge dip at the 800 mark is one of the huge dips that originally tipped off scientists that this was a freakin’ weird star. “It was off the charts,” says Montet.)

Benjamin T. Montet, Joshua D. Simon
KIC 8462852 is a superficially ordinary main sequence F star for which Kepler detected an unusual series of brief dimming events. We obtain accurate relative photometry of KIC 8462852 from the Kepler full frame images, finding that the brightness of KIC 8462852 monotonically decreased over the four years it was observed by Kepler. Over the first ~1000 days, KIC 8462852 faded approximately linearly at a rate of 0.341 +/- 0.041 percent per year, for a total decline of 0.9%. KIC 8462852 then dimmed much more rapidly in the next ~200 days, with its flux dropping by more than 2%. For the final ~200 days of Kepler photometry the magnitude remained approximately constant, although the data are also consistent with the decline rate measured for the first 2.7 yr. Of a sample of 193 nearby comparison stars and 355 stars with similar stellar parameters, 0.6% change brightness at a rate as fast as 0.341 +/- 0.041 percent per year, and none exhibit either the rapid decline by >2% or the cumulative fading by 3% of KIC 8462852. We examine whether the rapid decline could be caused by a cloud of transiting circumstellar material, finding while such a cloud could evade detection in sub-mm observations, the transit ingress and duration cannot be explained by a simple cloud model. Moreover, this model cannot account for the observed longer-term dimming. No known or proposed stellar phenomena can fully explain all aspects of the observed light curve.

Read more at https://arxiv.org/pdf/1608.01316v1.pdf
Read also: SCIENTISTS IN THE DARK OVER YEARS-LONG DIMMING OF ‘ALIEN MEGASTRUCTURE STAR’

GW151226: Observation of Gravitational Waves from a 22 Solar-mass Binary Black Hole Coalescence

Figure 1. (Adapted from figure 1 of our publication). The gravitational wave event GW151226 as observed by the twin Advanced LIGO instruments: LIGO Hanford (left) and LIGO Livingston (right). The images show the data recorded by the detectors during the last second before merger as the signal varies as a function of time (in seconds) and frequency (in Hertz or the number of wave cycles per second). To be certain that a real gravitational wave has been observed, we compare the data from the detectors against a pre-defined set of models for merging binaries. This allows us to find gravitational wave signals which are buried deep in the noise from the instruments and nearly impossible to find by eye. The animation shows the detector data with and without removing the best-matching model gravitational-wave signal, making it much easier to identify. The signal can be seen sweeping up in frequency as the two black holes spiral together. This signal is much more difficult to spot by eye than the first detection GW150914!

Figure 1. (Adapted from figure 1 of our publication). The gravitational wave event GW151226 as observed by the twin Advanced LIGO instruments: LIGO Hanford (left) and LIGO Livingston (right). The images show the data recorded by the detectors during the last second before merger as the signal varies as a function of time (in seconds) and frequency (in Hertz or the number of wave cycles per second). To be certain that a real gravitational wave has been observed, we compare the data from the detectors against a pre-defined set of models for merging binaries. This allows us to find gravitational wave signals which are buried deep in the noise from the instruments and nearly impossible to find by eye. The animation shows the detector data with and without removing the best-matching model gravitational-wave signal, making it much easier to identify. The signal can be seen sweeping up in frequency as the two black holes spiral together. This signal is much more difficult to spot by eye than the first detection GW150914!

A few months after the first detection of gravitational waves from the black hole merger event GW150914, the Laser Interferometer Gravitational-Wave Observatory (LIGO) has made another observation of gravitational waves from the collision and merger of a pair of black holes. This signal, called GW151226, arrived at the LIGO detectors on 26 December 2015 at 03:38:53 UTC.

The signal, which came from a distance of around 1.4 billion light-years, was an example of a compact binary coalescence, when two extremely dense objects merge. Binary systems like this are one of many sources of gravitational waves for which the LIGO detectors are searching. Gravitational waves are ripples in space-time itself and carry energy away from such a binary system, causing the two objects to spiral towards each other as they orbit. This inspiral brings the objects closer and closer together until they merge. The gravitational waves produced by the binary stretch and squash space-time as they spread out through the universe. It is this stretching and squashing that can be detected by observatories like Advanced LIGO, and used to reveal information about the sources which created the gravitational waves.

GW151226 is the second definitive observation of a merging binary black hole system detected by the LIGO Scientific Collaboration and Virgo Collaboration. Together with GW150914, this event marks the beginning of gravitational-wave astronomy as a revolutionary new means to explore the frontiers of our Universe….

Read more at: http://www.ligo.org/science/Publication-GW151226/index.php#sthash.GM0EB4ib.dpuf>

March 13, 1930: Clyde Tombaugh’s discovery of Pluto announced

pluto_chicago dailyIn early 1930, Pluto was discovered by a farm boy from Kansas with no formal training in astronomy. The announcement in March of Pluto’s discovery was a moment of excitement for both scientists and the public.

Clyde Tombaugh was born on February 4, 1906 in Illinois, and grew up on a farm in Kansas. He became interested in astronomy as a teenager after observing craters on the moon and rings around Saturn through his uncle’s three inch telescope. The family soon ordered a better telescope to encourage their son’s interests. When he was 20, Clyde Tombaugh began building his own telescopes.

By 1928 Tombaugh had built his third backyard telescope and used it to make drawings of Mars and Jupiter. He sent these to Vesto M. Slipher, the director of the Lowell Observatory in Flagstaff, Arizona, asking for comments. After a short correspondence, Slipher offered him a job at the observatory. His task would be to search for “Planet X.”

Clyde W. Tombaugh at the door of the Pluto discovery telescope, Lowell Observatory, Arizona (Photo courtesy of Lowell Observatory Archives)

Clyde W. Tombaugh at the door of the Pluto discovery telescope, Lowell Observatory, Arizona (Photo courtesy of Lowell
Observatory Archives)

Planet X had been predicted by Percival Lowell. Lowell, a businessman and astronomer known for his belief that a network of canals existed on Mars and was evidence of an intelligent alien civilization, built the Lowell Observatory to prove his theory. But as it became more and more clear that there was no evidence for that theory, he began to focus on searching for a new planet. Lowell had observed some peculiarity in the orbits of Neptune and Uranus and figured there must be another planet with a mass comparable to Neptune’s orbiting the sun beyond Neptune. Lowell searched for the planet, which he called Planet X, from 1905 to his death in 1916.

For years after Lowell’s death, the Lowell observatory was hampered by an expensive legal battle with Lowell’s widow. In 1927 the observatory was ready to resume the search for Planet X, and it acquired a new 13 inch refracting telescope for the search.

Slipher assigned the task to Tombaugh, who arrived in Flagstaff in January 1929. First, he had to use the telescope to make many photographic plates, systematically taking pictures of regions of the night sky where the new planet might appear. For each region, Tombaugh made two photos, taken several days apart. He spent many cold nights in the unheated observatory dome carefully making the observations.

After creating many such pairs of plates, he would compare the two members of each pair. Distant stars would appear in the same position on both plates, but a planet would have moved in the several days between the two exposures. Tombaugh used a device called a blinking comparator to make the comparison. The device would present him with sections of the two photo plates to be compared, shifting between the two several times a second. Most of the time the photos were the same and Tombaugh would see nothing, but if an object had moved between the two exposures, Tombaugh would see a blink.

It was incredibly tedious work requiring intense concentration, but Tombaugh greatly preferred it to going back to work on the farm, so he persisted.

After months of searching, he had found several asteroids, but nothing that fit the criteria for Planet X. Finally, in February 1930, while scanning the plates he had taken a few weeks earlier, he saw something that moved. He determined that the object had moved about 3 mm on the plates between the two exposures, indicating an orbital distance of about 40-43 AU, putting it outside the orbit of Neptune at about the right place to be the predicted planet.

Tombaugh told Slipher he had found Planet X, and on March 13, 1930, the Observatory announced the finding of the new object. The announcement date was chosen to coincide with both the anniversary of Herschel’s discovery of Uranus in 1781 and Percival Lowell’s birthday in 1855.

The public and astronomers were enthusiastic about the new planet. Later that month the object was officially named Pluto, after the Roman god of the underworld, who could make himself invisible. The name was suggested by an 11 year old girl in England. A secondary reason for the name was that the first two letters are Percival Lowell’s initials.

Though exciting, the planet was tiny, just a dot on the photograph, and some astronomers doubted whether it was massive enough to affect the orbit of Uranus and Neptune.

Pluto’s mass was not known until 1978, when its moon Charon was discovered. Pluto’s mass is about 0.002 that of Earth, making it much too small to influence the orbit of Neptune.

Ultimately, Pluto lost its planet status. Other objects in the neighborhood of Pluto have been discovered in recent years, including several comparable in size to Pluto. In 2006, much to the disappointment of children around the world, the International Astronomical Union redefined the term “planet.” The new definition of a planet requires an object to orbit a star, be large enough to be made round by gravity, and have cleared its orbit of other debris. The third criterion disqualifies Pluto, which is now known as a dwarf planet.

After the discovery of Pluto, Tombaugh received a scholarship to study astronomy at the University of Kansas. He began as a freshman in 1932 and continued to work in astronomy for many years. Tombaugh was later known as one of only a few scientists to take UFOs seriously. He died in 1997, mercifully before the demotion of his planet to the status of a dwarf.

Read more at www.aps.org

Eavesdropping on aliens

A small band in the sky has been identified in which extraterrestrial astronomers have good chances of discovering Earth

Narrow band: the image illustrates the transit zone, in which distant observers could see the Earth pass in front of the Sun. © Axel Quetz (MPIA) / Axel Mellinger, Central Michigan University

Narrow band: the image illustrates the transit zone, in which distant observers could see the Earth pass in front of the Sun.
© Axel Quetz (MPIA) / Axel Mellinger, Central Michigan University

Are we alone in the universe? To answer this question, astronomers have been using a variety of methods in the past decades to search for habitable planets and for the signals from extraterrestrial observers – to date, with no success. Maybe the search strategy has not been optimized until now, say researchers from the Max Planck Institute for Solar System Research in Göttingen and from McMaster University in Canada. They suggest that future searches focus on that part of the sky in which potential distant observers of the planetary system can notice the yearly transit of the Earth in front of the Sun. Continue reading Eavesdropping on aliens