Astronomers get first peek into core of supernova, using NuSTAR telescope

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Astronomers for the first time have peered into the heart of an exploding star in the final minutes of its existence.The feat is one of the primary goals of NASA’s NuSTAR mission, launched in June 2012 to measure high-energy X-ray emissions from exploding stars, or supernovae, and black holes, including the massive black hole at the center of our Milky Way Galaxy.The NuSTAR team reported in this week’s issue of the journal Nature the first map of titanium thrown out from the core of a star that exploded in 1671. That explosion produced the beautiful supernova remnant known as Cassiopeia A (Cas A).The well-known supernova remnant has been photographed by many optical, infrared and X-ray telescopes in the past, but these revealed only how the star’s debris collided in a shock wave with the surrounding gas and dust and heated it up. NuSTAR has produced the first map of high-energy X-ray emissions from material created in the actual core of the exploding star: the radioactive isotope titanium-44, which was produced in the star’s core as it collapsed to a neutron star or black hole. The energy released in the core collapse supernova blew off the star’s outer layers, and the debris from this explosion has been expanding outward ever since at 5,000 kilometers per second.”This has been a holy grail observation for high energy astrophysics for decades,” said coauthor and NuSTAR investigator Steven Boggs, UC Berkeley professor and chair of physics. “For the first time we are able to image the radioactive emission in a supernova remnant, which lets us probe the fundamental physics of the nuclear explosion at the heart of the supernova like we have never been able to do before.”"Supernovae produce and eject into the cosmos most of the elements are important to life as we know it,” said UC Berkeley professor of astronomy Alex Filippenko, who was not part of the NuSTAR team. “These results are exciting because for the first time we are getting information about the innards of these explosions, where the elements are actually produced.”Boggs says that the information will help astronomers build three-dimensional computer models of exploding stars, and eventually understand some of the mysterious characteristics of supernovae, such as jets of material ejected by some. Previous observations of Cas A by the Chandra X-ray telescope, for example, showed jets of silicon emerging from the star.”Stars are spherical balls of gas, and so you might think that when they end their lives and explode, that explosion would look like a uniform ball expanding out with great power,” said Fiona Harrison, the principal investigator of NuSTAR at the California Institute of Technology. “Our new results show how the explosion’s heart, or engine, is distorted, possibly because the inner regions literally slosh around before detonating.”Expanding supernova remnantCas A is about 11,000 light years from Earth and the most studied nearby supernova remnant. In the 343 years since the star exploded, the debris from the explosion has expanded to about 10 light years across, essentially magnifying the pattern of the explosion so that it can be seen from Earth.Earlier observations of the shock-heated iron in the debris cloud led some astronomers to think that the explosion was symmetric, that is, equally powerful in all directions. Boggs noted, however, that the origins of the iron are so unclear that its distribution may not reflect the explosion pattern from the core.”We don’t know whether the iron was produced in the supernova explosion, whether it was part of the star when it originally formed, if it is just in the surrounding material, or even if the iron we see represents the actual distribution of iron itself, because we wouldn’t see it if it were not heated in the shock,” he said.The new map of titanium-44, which does not match the distribution of iron in the remnant, strongly suggests that there is cold iron in the interior that Chandra does not see. …


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How stellar death can lead to twin celestial jets

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Astronomers know that while large stars can end their lives as violently cataclysmic supernovae, smaller stars end up as planetary nebulae — colourful, glowing clouds of dust and gas. In recent decades these nebulae, once thought to be mostly spherical, have been observed to often emit powerful, bipolar jets of gas and dust. But how do spherical stars evolve to produce highly aspherical planetary nebulae?In a theoretical paper published this week in the Monthly Notices of the Royal Astronomical Society, a University of Rochester professor and his undergraduate student conclude that only “strongly interacting” binary stars — or a star and a massive planet — can feasibly give rise to these powerful jets.When these smaller stars run out of hydrogen to burn they begin to expand and become Asymptotic Giant Branch (AGB) stars. This phase in a star’s life lasts at most 100,000 years. At some point some of these AGB stars, which represent the distended last spherical stage in the lives of low mass stars, become “pre-planetary” nebula, which are aspherical.”What happens to change these spherical AGB stars into non-spherical nebulae, with two jets shooting out in opposite directions?” asks Eric Blackman, professor of physics and astronomy at Rochester. “We have been trying to come up with a better understanding of what happens at this stage.”For the jets in the nebulae to form, the spherical AGB stars have to somehow become non-spherical and Blackman says that astronomers believe this occurs because AGB stars are not single stars but part of a binary system. The jets are thought to be produced by the ejection of material that is first pulled and acquired, or “accreted,” from one object to the other and swirled into a so-called accretion disk. There are, however, a range of different scenarios for the production of these accretion disks. All these scenarios involve two stars or a star and a massive planet, but it has been hard to rule any of them out until now because the “core” of the AGBs, where the disks form, are too small to be directly resolved by telescopes. Blackman and his student, Scott Lucchini, wanted to determine whether the binaries can be widely separated and weakly interacting, or whether they must be close and strongly interacting.By studying the jets from pre-planetary and planetary nebulae, Blackman and Lucchini were able to connect the energy and momentum involved in the accretion process with that in the jets; the process of accretion is what in effect provides the fuel for these jets. …


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Loneliness is a major health risk for older adults

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Feeling extreme loneliness can increase an older person’s chances of premature death by 14 percent, according to research by John Cacioppo, professor of psychology at the University of Chicago.Cacioppo and his colleagues’ work shows that the impact of loneliness on premature death is nearly as strong as the impact of disadvantaged socioeconomic status, which they found increases the chances of dying early by 19 percent. A 2010 meta-analysis showed that loneliness has twice the impact on early death as does obesity, he said.Cacioppo, the Tiffany & Margaret Blake Distinguished Service Professor in Psychology at the University, joined other scholars at a seminar on “The Science of Resilient Aging” Feb. 16 at the American Association for the Advancement of Science Annual meeting in Chicago.The researchers looked at dramatic differences in the rate of decline in physical and mental health as people age. Cacioppo and colleagues have examined the role of satisfying relationships on older people to develop their resilience, the ability to bounce back after adversity and grow from stresses in life.The consequences to health are dramatic, as feeling isolated from others can disrupt sleep, elevate blood pressure, increase morning rises in the stress hormone cortisol, alter gene expression in immune cells, and increase depression and lower overall subjective well-being, Cacioppo pointed out in a talk, “Rewarding Social Connections Promote Successful Aging.”Cacioppo, one of the nation’s leading experts on loneliness, said older people can avoid the consequences of loneliness by staying in touch with former co-workers, taking part in family traditions, and sharing good times with family and friends — all of which gives older adults a chance to connect others about whom they care and who care about them.”Retiring to Florida to live in a warmer climate among strangers isn’t necessarily a good idea if it means you are disconnected from the people who mean the most to you,” said Cacioppo. Population changes make understanding the role of loneliness and health all the more important, he explained.”We are experiencing a silver tsunami demographically. The baby boomers are reaching retirement age. Each day between 2011 and 2030, an average of 10,000 people will turn 65,” he said. “People have to think about how to protect themselves from depression, low subjective well-being and early mortality.”Although some people are happy to be alone, most people thrive from social situations in which they provide mutual support and develop strong rapport. Evolution encouraged people to work together to survive and accordingly most people enjoy companionship over being alone.Research by Cacioppo and his colleagues has identified three core dimensions to healthy relationships — intimate connectedness, which comes from having someone in your life you feel affirms who you are; relational connectedness, which comes from having face-to-face contacts that are mutually rewarding; and collective connectedness, which comes from feeling that you’re part of a group or collective beyond individual existence.It is not solitude or physical isolation itself, but rather the subjective sense of isolation that Cacioppo’s work shows to be so profoundly disruptive. Older people living alone are not necessary lonely if they remain socially engaged and enjoy the company of those around them. …


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