From SPACE.com: “Bizarre 3-Year-Long Supernova Defies Our Understanding of How Stars Die”

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SPACE.com

November 8, 2017
Harrison Tasoff

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A massive star reaches the end of its life in an artist’s conception of a supernova. Credit: M. Kornmesser/ESO

The appearance of a years-long supernova explosion challenges scientist’s current understanding of star formation and death, and work is underway to explain the bizarre phenomenon.

Stars more than eight times the mass of the sun end their lives in fantastic explosions called supernovas. These are among the most energetic phenomena in the universe. The brightness of a single dying star can briefly rival that of an entire galaxy. Supernovas that form from supermassive stars typically rise quickly to a peak brightness and then fade over the course of around 100 days as the shock wave loses energy.

In contrast, the newly analyzed supernova iPTF14hls grew dimmer and brighter over the span of more than two years, according to a statement by Las Cumbres Observatory [based] in Goleta, California, which tracked the object. Details of the discovery appeared on Nov. 8 in the journal Nature.

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Las Cumbres Observatory Global Telescope Network 1-meter telescope node at Cerro Telolo, Chile

An inconspicuous discovery

Supernova iPTF14hls was unremarkable when first detected by a partner telescope in San Diego on Sept. 22, 2014. The light spectrum was a textbook example of a Type II-P supernova, the most common type astronomers see, lead author Iair Arcavi, an astronomer at the University of California, Santa Barbara, told Space.com. And the supernova looked like it was already fading, he said.

The observatory was in the middle of a 7.5-year collaborative survey, so Arcavi focused on more-promising objects. But in February, 2015, Zheng Chuen Wong, a student working for Arcavi that winter, noticed the object had become brighter over the past five months.

“He showed me the data,” Arcavi said, “and he [asked], ‘Is this normal?’ and I said, ‘Absolutely not. That is very strange. Supernovae don’t do that,'” Arcavi said.

At first, Arcavi thought it might be a local star in our galaxy, which would appear brighter because it was closer, he said. Many stars are also known to have variable brightness. But the light signature revealed that the object was indeed located in a small, irregular galaxy about 500 million light-years from Earth.

And the object only got weirder. After 100 days, the supernova looked just 30 days old. Two years later, the supernova’s spectrum still looked the way it would if the explosion were only 60 days old. The supernova recently emerged from behind Earth’s sun, and Arcavi said it’s still bright, after roughly three years. But at one one-hundredth of its peak brightness, the object appears to finally be fading out.

“Just to be clear, though, there is no existing model or theory that explains all of the observations we have,” said Arcavi. The supernova may fade out; it may grow brighter, or it may suddenly disappear.

One reason for Arcavi’s uncertainty is that a supernova was seen in the same location in 1954. This means that the event Acavi has been observing, whatever it is, may actually be 60 years running. There’s a 1 to 5 percent chance the two events are unrelated, but that would be even more surprising, said Arcavi. Astronomers have never observed unrelated supernova in the same place decades apart. “We are beyond the cutting-edge of models,” Arcavi said.

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Supernova iPTF14hls dwarfs typical supernovas in both brightness and longevity. And the event’s dramatic fluctuations pose an exciting challenge for the astronomical community to explain.
Credit: Credit: S. Wilkinson/LCO

Beyond cutting edge

“I’m not sure, and I don’t think anyone else is sure, just what the hell is happening,” astrophysicist Stanford Woosley, at University of California, Santa Cruz, told Space.com. “And yet it happened, and so it begs explanation.”

Woosley is not affiliated with the study, but he is among the theoreticians working to understand the event. Two hypotheses show promise in explaining it, he said.

The first involves the famous equation E = mc2. With this formula , Albert Einstein demonstrated that matter and energy are fundamentally interchangeable. Stars burn by converting matter into energy, fusing lighter elements like hydrogen and helium into heavier elements, which build up in the star’s core and also release energy. When a star more than 80 times the mass of the sun reaches a temperature of 1 billion degrees Celsius (1.8 billion degrees Fahrenheit), this energy-matter equivalence produces pairs of electrons and their antiparticle counterparts, positrons, Woosley said. The process robs the star of energy, and so the object shrinks.

But as this happens, the temperature rises in the star’s core. At 3 billion C (5.4 billion F), oxygen fuses explosively, blowing off massive amounts of material and resetting the cycle. This process repeats until the star reaches a stable mass, explained Woosley. When the front of an ejected shell of material hits the trailing edge of a previous shell, it releases energy as light.

The star continues to fuse oxygen and the elements of greater masses, up until iron, at which point the reaction fails to release enough energy to keep the star from collapsing in on itself.Eventually, a star like the one that gave rise to iPTF14hls will collapse into a black hole without another explosion, said Woosley.

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This image depicts a simulated collision between two shells of matter ejected by subsequent pulsation pair instability supernova explosions.
Credit: Ke-Jung Chen/School of Physics and Astronomy, University of Minnesota

This phenomenon, called a pulsation pair instability (PPI) supernova, could account for iPTF14hls’ sustained luminosity as well as the object’s varying brightness. This explanation would require the star to have been 105 times the mass of the sun, said Woosley. However, the PPI model cannot account for the tremendous amount of energy iPTF14hls has released. The first explosion of 2014 had more energy than the model predicts for all the explosions combined, said Arcavi.

What’s more, this phenomenon has yet to be verified observationally. “Stars between 80 and 140 solar masses, which do this kind of thing, have to exist,” said Woosley, “and they have to die, and so, somewhere, this has to be going on.” But no one has seen it yet, he said.

A magnetic superstorm

An alternative explanation involves a star 20 to 30 times the mass of Earth’s sun. After a more conventional supernova, such a star could have condensed into a rapidly spinning neutron star, called a magnetar.

A neutron star packs the mass of 1.5 suns into an object with a diameter about the size of New York City. A neutron star rotating at 1,000 times per second would have more energy than a supernova, according to Woosley. It would also generate a magnetic field 100 trillion to 1 quadrillion times the strength of Earth’s field. As the star spun down over the course of several months, its incredible magnetic field could transfer the star’s rotational energy into the remnants of the supernova that it formed from, releasing light, Woosley explained.

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An artist depicts a magnetar in the star cluster Westerlund 1. The luminous arcs follow the object’s intense magnetic field. Credit: L. Calçada/ESO

“It’s like there’s a lighthouse down in the middle of the supernova,” said Woolsey.

But the magnetar explanation is not perfect, either. It has trouble explaining the dips and peaks in iPTF14hls’ brightness, and the physics behind how such a phenomenon might work is still uncertain, said Woosley.

As iPTF14hls sheds energy, Arcavi said he hopes to be able to see deeper into the object’s structure. If it is a magnetar, then he expects to see X-rays, previously obscured by the supernova itself, beginning to break through, he said. “Maybe by combining pulsation pair instability with [a magnetar], you can start to explain the supernova,” Arcavi said.

Keeping busy while keeping watch

The existence of iPTF14hls has far-reaching implications, the researchers said. At 500 million light-years away, the supernova is still relatively close to Earth, and the universe is practically the same today — in terms of composition and organization —as it was when this event occurred, according to Arcavi. If the event was a PPI supernova, it tells astronomers that stars more than 100 times the mass of the sun — thought to be more prevalent in the early universe — are still forming today.

The event also had far more hydrogen than researchers expected to see. The explosion in 1954 should have expelled nearly all of the star’s hydrogen, said Arcavi. Astrophysicists will have to revisit their models of supernovas to understand how this can occur, he said.

The finding has ramifications for the study of galaxies as well. “The energy of the gravity that’s keeping that galaxy together is about the same order of magnitude as the energy that was released in the supernova,” Arcavi said. “So, a few of these in a galaxy could actually unbind the entire galaxy.”

Arcavi and his team plan to continue monitoring iPTF14hls for at least one to two years. And a suite of international telescopes and observatories will join the effort. Swedish colleagues at the Nordic Optical Telescope, in the Canary Islands, will track the object as it continues to dim beyond what Arcavi’s telescope array can detect. NASA’s Swift spacecraft will look for X-ray emissions, while the Hubble Space Telescope is scheduled to image the location beginning in December, and others will follow, Arcavi said.

For now, the event remains a mystery.

“It’s just a puzzle in the sky,” said Woosley. “That’s what we live for, what astronomers love.”

See the full article here .

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From UC Berkeley: “Climate policies study shows Inland Empire economic boon”

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UC Berkeley

August 3, 2017
Jacqueline Sullivan

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UC Berkeley researchers found that the proliferation of renewable energy plants — like the San Gorgonio Pass wind farm shown above — is responsible for over 90 percent of the direct benefit of California’s climate and clean energy policies in the Inland Empire. (iStock photo).

According to the first comprehensive study of the economic effects of climate programs in California’s Inland Empire, Riverside and San Bernardino counties experienced a net benefit of $9.1 billion in direct economic activity and 41,000 jobs from 2010 through 2016.

Researchers at UC Berkeley’s Center for Labor Research and Education and the Center for Law, Energy and the Environment at Berkeley Law report that many of these jobs were created by one-time construction investments associated with building renewable energy power plants. These investments, they say, helped rekindle the construction industry, which experienced major losses during the Great Recession.

When accounting for the spillover effects, the researchers report in their study commissioned by nonpartisan, nonprofit group Next 10, that state climate policies resulted in a total of $14.2 billion in economic activity and more than 73,000 jobs for the region during the same seven years.

Study focal points

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Inland Empire residents are at especially high risk for pollution-related health conditions. This hazy view from a Rancho Cucamonga street attests to the region’s smog problem. (Photo by Mikeetc via Creative Commons).

Because smog in San Bernardino and Riverside counties is consistently among the worst in the state, residents are at especially high risk of pollution-related health conditions.

“California has many at-risk communities — communities that are vulnerable to climate change, but also vulnerable to the policy solutions designed to slow climate change,” said Betony Jones, lead author of the report and associate director of the Green Economy Program at UC Berkeley’s Center for Labor Research and Education.

In the Inland Empire, per capita income is approximately $23,000, compared to the state average of $30,000, and 17.5 percent of the residents of Riverside and San Bernardino counties live below the poverty line, compared to 14.7 percent of all Californians.

The Net Economic Impacts of California’s Major Climate Programs in the Inland Empire study comes out right after the state’s recent decision to extend California’s cap-and-trade program, and as other states and countries look to California as a model.

Cap-and-trade

After accounting for compliance spending and investment of cap-and-trade revenue, researchers found cap and trade had net economic impacts of $25.7 million in San Bernardino and Riverside counties in the first four years of the program, from 2013 to 2016.

That includes $900,000 in increased tax revenue and net employment growth of 154 jobs through the Inland Empire economy. When funds that have been appropriated but have not yet been spent are included, projected net economic benefits reach nearly $123 million, with 945 jobs created and $5.5 million in tax revenue.

Proliferation of renewables

The researchers found that the proliferation of renewable energy plants is responsible for over 90 percent of the direct benefit of California’s climate and clean energy policies in the Inland Empire. As of October 2016, San Bernardino and Riverside Counties were home to more than 17 percent of the state’s renewable generation capacity, according the California Energy Commission.

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Researchers found that altogether, renewables like the solar panels pictured above, contributed more than 60,000 net jobs to the regional economy over seven years. (iStock photo)

“Even after accounting for construction that would have taken place in a business-as-usual scenario, new renewable power plants created the largest number of jobs in the region over the seven-year period, generating 29,000 high-skilled, high-quality construction jobs,” said Jones.

The authors compared the jobs created in the generation of renewable electricity with those that would have been created by maintaining natural gas electricity generation. “While renewables create fewer direct jobs, the multiplier effects are greater in the Inland Empire economy,” Jones said. “Altogether, renewable generation contributed over 60,000 net jobs to the regional economy over seven years.”

Rooftop solar, energy efficiency programs

The report looks at the costs and benefits of the California Solar Initiative, the federal renewables Investment Tax Credit, and investor-owned utility energy efficiency programs, which provide direct incentives for solar installation and energy efficiency retrofits at homes, businesses and institutions. These programs provided about $1.1 billion in subsidies for distributed solar and $612 million for efficiency in the Inland Empire between 2010 and 2016.

While researchers calculated benefits for these two programs separately, they identified the costs of these programs to electricity ratepayers together. When the benefits are weighed against these costs, the total net impact of both programs resulted in the creation of more than 12,000 jobs and $1.68 billion across the economy over the seven years studied.

The report’s authors suggest that officials and/or policymakers:

Develop a comprehensive program for transportation, the greatest challenge facing in California’s climate goals;
Expand energy efficiency programs to reduce energy use in the existing building and housing stock while reducing energy costs and creating jobs and economic activity;
Ensure that the Inland Empire receives appropriate statewide spending based on its economic and environmental needs;
Develop transition programs for workers and communities affected by the decline of the Inland Empire’s greenhouse gas-emitting industries.

“California continues to demonstrate leadership on climate and clean energy, and results like these show that California’s models can be exported,” said Ethan Elkind, climate director at the UC Berkeley Center for Law, Energy and the Environment.

Noel Perry, founder of Next 10, said the report gives policymakers and stakeholders the concrete data needed to weigh policy options and investments in the Inland Empire and beyond.

See the full article here .

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Founded in the wake of the gold rush by leaders of the newly established 31st state, the University of California’s flagship campus at Berkeley has become one of the preeminent universities in the world. Its early guiding lights, charged with providing education (both “practical” and “classical”) for the state’s people, gradually established a distinguished faculty (with 22 Nobel laureates to date), a stellar research library, and more than 350 academic programs.

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