tech geeks Physics

[Page Scrawler]

I found these videos on YouTube. Pretty interesting to see what dry ice does to a knife heated to 1,000* Fahrenheit as the blade cuts through the ice block.

 

 

 

[JamesSavik]

"Everybody Knew It Had To Be There" --Missing Half of Normal Matter in the Universe Has Been Detected

October 09, 2017

Daily Galaxy

 

 

“Everybody sort of knows that it has to be there, but this is the first time that somebody – two different groups, no less – has come up with a definitive detection,” says Ralph Kraft at the Harvard-Smithsonian Center for Astrophysics in Massachusetts.

Observations of galaxies and galaxy clusters in the local universe can account for only 10% of the baryon content -made of particles called baryons rather than dark matter- inferred from measurements of the cosmic microwave background and from nuclear reactions in the early Universe. Locating the remaining 90% of baryons has been one of the major challenges in modern cosmology. The missing links between galaxies have finally been found. This is the first detection of the roughly half of the normal matter in our universe – protons, neutrons and electrons – unaccounted for by previous observations of stars, galaxies and other bright objects in space.

 

Models of the universe say there should be about twice as much ordinary matter out there, compared with what we have observed so far. Now, two separate teams found the missing matter – made of particles called baryons rather than dark matter – linking galaxies together through filaments of hot, diffuse gas.

“The missing baryon problem is solved,” says Hideki Tanimura at the Institute of Space Astrophysics in Orsay, France, leader of one of the groups. The other team was led by Anna de Graaff at the University of Edinburgh, UK.

“There’s no sweet spot – no sweet instrument that we’ve invented yet that can directly observe this gas,” says Richard Ellis at University College London. “It’s been purely speculation until now.” Because it's not quite hot enough for X-ray telescopes to observe.

Both teams took advantage of a phenomenon called the Sunyaev-Zel’dovich effect that occurs when light left over from the big bang passes through hot gas to find another way to definitively show that these threads of gas are really there. As photons of light travel, some of them scatters off the electrons in the gas, leaving a dim patch in the cosmic microwave background from the birth of the cosmos that were to faint to be mapped by the Planck satellite in 2015.

Both teams selected pairs of galaxies from the Sloan Digital Sky Survey that were expected to be connected by a strand of baryons. They stacked the Planck signals for the areas between the galaxies, making the individually faint strands detectable en masse.

Tanimura’s team stacked data on 260,000 pairs of galaxies, and de Graaff’s group used over a million pairs revealing firm evidence of gas filaments between the galaxies. Tanimura’s group found they were almost three times denser than the mean for normal matter in the universe, and de Graaf’s group found they were six times denser confirming that the gas in these areas is dense enough to form filaments.

“We expect some differences because we are looking at filaments at different distances,” says Tanimura. “If this factor is included, our findings are very consistent with the other group.”

“This goes a long way toward showing that many of our ideas of how galaxies form and how structures form over the history of the universe are pretty much correct,” says Ralph Kraft.

 

Journal references: arXiv, 1709.05024 and 1709.10378v1

The Daily Galaxy via New Scientist and NextBig Future  and ARXIV.org 

[JamesSavik]

A Kilonova Detected --"A Cosmic Phenomenon Long Theorized But Never Conclusively Observed — Until Now"

Daily Galaxy

October 16, 2017

 

 

In the world of astrophysics, Aug. 17, 2017, was a red-letter day. “This is a game-changer for astrophysics,” said UC Santa Barbara faculty member Andy Howell, who leads the supernova group at the Las Cumbres Observatory (LCO). “A hundred years after Einstein theorized gravitational waves, we’ve seen them and traced them back to their source to find an explosion with new physics of the kind we’ve only dreamed about.”

First, NASA’s orbiting Fermi satellite identified a burst of high-energy gamma rays. Then, in the minute leading up to the Fermi burst, scientists noticed microscopic distortions in space caused by gravitational waves passing through the Earth. When they combined the data from the two Laser Interferometer Gravitational-Wave Observatory (LIGO) facilities in Hanford, Washington, and Livingston, Louisiana, with the data from the Virgo detector in Italy, they realized they could localize the disturbance to a relatively small region of the sky — only about 150 times the size of the full moon — near the constellation Hydra.

 

Astronomers at Las Cumbres Observatory (LCO) in Santa Barbara activated their robotic network of 20 telescopes around the world and were one of six teams to co-discover a new source of light in that region and localize it to the galaxy NGC 4993, only about 130 million light years away.

“Such a gravitational wave signal had never been seen before but was unmistakably generated by two neutron stars spiraling together,” explained Iair Arcavi, a NASA Einstein postdoctoral fellow in UC Santa Barbara’s Department of Physics and leader of the LCO follow-up effort. The resultant study appears in the journal Nature.

The outburst that occurs right after two neutron stars merge is called a kilonova, a phenomenon that had long been theorized though never conclusively observed — until now. Unlike traditional ground-based facilities with single telescopes, the LCO network could observe the phenomenon every few hours for five consecutive days. During that time, the light from the explosion dimmed by a factor of 20, fading at an unprecedented rate for something so luminous.

“This marks the first time in history that an astronomical phenomenon has been first sensed through gravitational waves and then seen with telescopes,” Arcavi said. “For years, we’ve heard theorists predict how a kilonova should look. I couldn’t believe we were finally seeing one for the first time.”

Kilonovae are thought to be the primary source of all the elements heavier than iron in the universe. For example, most of the gold on Earth may have been created in a kilonova. The name originates from the prediction that a kilonova would be a thousand times brighter than a nova, though dimmer than a supernova.

“We know now that one reason they had been so elusive is that they fade too quickly for conventional astronomical facilities to detect,” Arcavi said.

“Thanks to knowing where to look and then having telescopes networked together all around the world, we were able to watch this new type of cosmic explosion rise and fade in real time,” said co-author Curtis McCully, a postdoctoral researcher at LCO and in the UCSB Department of Physics. “This is a remarkable story of the advent of gravitational wave astronomy combined with robotic internet-based optical astronomy.”

LCO astronomers also used their and other facilities around the world, including the 8-meter Gemini telescope in Chile, to split the light of the kilonova into its chromatic components: a rainbow. McCully led this study, which appears in The Astrophysical Journal Letters.

“We found that only a tiny amount of material was ejected in the explosion —only about 1 percent of the total matter in the system,” he noted. “The material was also flung out at an extraordinary speed, as much as 30 percent of the speed of light.”

The LCO group also contributed to a third study measuring the Hubble constant, which characterizes the expansion rate of the universe. That research used the inspiraling neutron stars as “standard sirens” to determine their distance from Earth and compared that distance to the redshift, or how much light has been stretched by the expansion of the universe. That study appears in the journal Nature.

The Daily Galaxy via UC Santa Barbara

[JamesSavik]

"An Epic First!" --ESO's Fleet of Telescopes in Chile Detect Visible Explosion of Colliding Neutron Stars (WATCH Video)

October 16, 2017

Daily Galaxy

 

 

ESO’s fleet of telescopes in Chile have detected the first visible counterpart to a gravitational wave source. These historic observations suggest that this unique object is the result of the merger of two neutron stars. The cataclysmic aftermaths of this kind of merger — long-predicted events called kilonovae — disperse heavy elements such as gold and platinum throughout the Universe. This discovery, published in several papers in the journal Nature and elsewhere, also provides the strongest evidence yet that short-duration gamma-ray bursts are caused by mergers of neutron stars.

For the first time ever, astronomers have observed both gravitational waves and light (electromagnetic radiation) from the same event, thanks to a global collaborative effort and the quick reactions of both ESO’s facilities and others around the world.

 

On 17 August 2017 the NSF's Laser Interferometer Gravitational-Wave Observatory (LIGO) in the United States, working with the Virgo Interferometer in Italy, detected gravitational waves passing the Earth. This event, the fifth ever detected, was named GW170817. About two seconds later, two space observatories, NASA’s Fermi Gamma-ray Space Telescope and ESA’s INTErnational Gamma Ray Astrophysics Laboratory (INTEGRAL), detected a short gamma-ray burst from the same area of the sky.

 

 

 

 

The LIGO–Virgo observatory network positioned the source within a large region of the southern sky, the size of several hundred full Moons and containing millions of stars [1]. As night fell in Chile many telescopes peered at this patch of sky, searching for new sources. These included ESO’s Visible and Infrared Survey Telescope for Astronomy (VISTA) and VLT Survey Telescope (VST) at the Paranal Observatory, the Italian Rapid Eye Mount (REM) telescope at ESO’s La Silla Observatory, the LCO 0.4-meter telescope at Las Cumbres Observatory, and the American DECam at Cerro Tololo Inter-American Observatory. The Swope 1-metre telescope was the first to announce a new point of light. It appeared very close to NGC 4993, a lenticular galaxy in the constellation of Hydra, and VISTA observations pinpointed this source at infrared wavelengths almost at the same time. As night marched west across the globe, the Hawaiian island telescopes Pan-STARRS and Subaru also picked it up and watched it evolve rapidly.

“There are rare occasions when a scientist has the chance to witness a new era at its beginning,” said Elena Pian, astronomer with INAF, Italy, and lead author of one of the Nature papers. “This is one such time!”

 

 

 

ESO launched one of the biggest ever “target of opportunity” observing campaigns and many ESO and ESO-partnered telescopes observed the object over the weeks following the detection [2]. ESO’s Very Large Telescope (VLT), New Technology Telescope (NTT), VST, the MPG/ESO 2.2-metre telescope, and the Atacama Large Millimeter/submillimeter Array (ALMA) [3] all observed the event and its after-effects over a wide range of wavelengths. About 70 observatories around the world also observed the event, including the NASA/ESA Hubble Space Telescope.

Distance estimates from both the gravitational wave data and other observations agree that GW170817 was at the same distance as NGC 4993, about 130 million light-years from Earth. This makes the source both the closest gravitational wave event detected so far and also one of the closest gamma-ray burst sources ever seen [4].

The ripples in spacetime known as gravitational waves are created by moving masses, but only the most intense, created by rapid changes in the speed of very massive objects, can currently be detected. One such event is the merging of neutron stars, the extremely dense, collapsed cores of high-mass stars left behind after supernovae [5]. These mergers have so far been the leading hypothesis to explain short gamma-ray bursts. An explosive event 1000 times brighter than a typical nova — known as a kilonova — is expected to follow this type of event.

The almost simultaneous detections of both gravitational waves and gamma rays from GW170817 raised hopes that this object was indeed a long-sought kilonova and observations with ESO facilities have revealed properties remarkably close to theoretical predictions. Kilonovae were suggested more than 30 years ago but this marks the first confirmed observation.

Following the merger of the two neutron stars, a burst of rapidly expanding radioactive heavy chemical elements left the kilonova, moving as fast as one-fifth of the speed of light. The colour of the kilonova shifted from very blue to very red over the next few days, a faster change than that seen in any other observed stellar explosion.

“When the spectrum appeared on our screens I realised that this was the most unusual transient event I’d ever seen,” remarked Stephen Smartt, who led observations with ESO’s NTT as part of the extended Public ESO Spectroscopic Survey of Transient Objects (ePESSTO) observing programme. “I had never seen anything like it. Our data, along with data from other groups, proved to everyone that this was not a supernova or a foreground variable star, but was something quite remarkable.”

Spectra from ePESSTO and the VLT’s X-shooter instrument suggest the presence of caesium and tellurium ejected from the merging neutron stars. These and other heavy elements, produced during the neutron star merger, would be blown into space by the subsequent kilonova. These observations pin down the formation of elements heavier than iron through nuclear reactions within high-density stellar objects, known as r-process nucleosynthesis, something which was only theorised before.

“The data we have so far are an amazingly close match to theory. It is a triumph for the theorists, a confirmation that the LIGO–VIRGO events are absolutely real, and an achievement for ESO to have gathered such an astonishing data set on the kilonova,” adds Stefano Covino, lead author of one of the Nature Astronomy papers.

“ESO’s great strength is that it has a wide range of telescopes and instruments to tackle big and complex astronomical projects, and at short notice. We have entered a new era of multi-messenger astronomy!” concludes Andrew Levan, lead author of one of the papers.

The Daily Galaxy via ESO