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This Star Has Exploded Annually For Millions of Years

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star in andromeda galaxy explodes

GK Persei, seen above, is a prime example of a nova remnant. Unlike supernovae, which blow stars apart from within, novae explosions occur on the surfaces of accreting white dwarfs. Though the previous record for largest nova remnant is about 3.5 light-years wide, researchers recently discovered M31N 2008-12a, a nova remnant that spans over 400 light-years.
(Credit: X-ray: NASA/CXC/RIKEN/D.Takei et al; Optical: NASA/STScI; Radio: NRAO/VLA)

Astronomers have discovered a star in the Andromeda galaxy that has been regularly erupting for the past million years, leaving behind one of the biggest shells of ejected material scientists have ever seen.

The new research, which was published last month in the journal Nature, not only marks the first discovery of such a super-remnant in another galaxy, it also paves the way for detecting a potentially massive population of repeatedly exploding stars, called recurrent novae, which may help shed light on how the universe has changed over time.

Swing Your Partner

The star responsible for this expansive remnant, which stretches over 400 light-years across, is actually from one of the most diminutive types of star: a white dwarf. These stellar corpses are left behind after a smallish star dies and blows off its outer layers, leaving behind only its dense core.

But in the case of this remnant, catchily named M31N 2008-12a, the culprit is not your ordinary white dwarf. This tiny star has a dance partner.

As the white dwarf and its nearby companion star orbit each other, the white dwarf rapidly siphons hydrogen from its buddy. As this unspent hydrogen fuels reaches the surface, it’s heated and compressed thanks to the white dwarf’s intense gravitational pull. Eventually, the hydrogen reaches a breaking point and spontaneously fuses to create helium, resulting in a powerful surface explosion we call a nova.

This burst of fusion causes the white dwarf to temporarily brighten up to a millionfold as it ejects material outward at about 3 percent the speed of light. In the case of M31N 2008-12a, over time, these repeated explosions have created an extensive and ever-expanding cocoon of gas and dust around the white dwarf.

According to the study, “Larger than almost all known remnant of even supernova explosions, the existence of this shell demonstrates that the nova M31N 2008-12a has erupted with high frequency for millions of years.”

It Keeps Going, and Going…

The massive size of the remnant is not its only claim to fame. Indeed, M31N 2008-12a also now holds the title of most frequently recurring nova, as it erupts at least once a year. “When we first discovered that M31N 2008-12a erupted every year, we were very surprised,” said co-author Allen Shafter of San Diego State University in a press release. This is because most recurrent novae only explode about once a decade.

But despite the fact that the white dwarf has spent the past million years or so exploding annually, researchers don’t think it will last forever. Once the white dwarf surpasses the Chandrasekhar limit — which is about 1.4 times the mass of the sun — it will irreparably blow itself apart as a supernova or collapse down into a neutron star.

According to theory, white dwarfs that are approaching the Chandrasekhar limit should undergo frequent novae explosions, resulting in gigantic remnants. And because that’s exactly what astronomers see happening around M31N 2008-12a, they think this star may be priming up for a supernova explosion itself. However, you and I likely will not be around to witness it.

“In less than 40,000 years,” the study says, “the underlying composition of the white dwarf will be revealed incontrovertibly when either a type Ia supernova or an accretion-induced collapse of the white dwarf to a neutron star is observed.”

If the researchers are able to find other examples of huge remnants around different novae, they think they may learn a bit about type Ia supernovae. Because type Ia supernovae have very predictable brightnesses (which is why they’re called standard candles), by studying them, researchers can pin down cosmic distances with extreme accuracy. Ultimately, this helps them better understand how the universe grows and evolves over time.

“They are, in effect, the measuring rods that allow us to map the visible universe,” said Shafter. “Despite their importance, we don’t fully understand where they come from.”

So for now, Shafter and his colleagues are working hard to determine whether super-remnants like M31N 2008-12a are the exception, or the rule. And if they’re as common as some think, then the next step becomes improving our ability to spot them.

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Ecology

Today’s letters: ‘Visionary’ plans don’t always work in Ottawa

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The opinion piece written by Tobi Nussbaum, CEO of the NCC, declares that a “bold, visionary transit plan” would showcase the capital.

As a long-term resident of Ottawa, I’ve had it with visionary plans. In the 1950s, the streetcars serving Ottawa so well were sent to the scrapyards. In the early ’60s, Queensway construction bulldozed established neighbourhoods and ripped the city apart. Later in the decade, the downtown railway station, which could have formed the hub of a commuter network, was relocated to the suburbs. These actions, in the name of “progress,” were undertaken with the “vision” to make Ottawa a car-reliant city.

Now we have an LRT, built just in time for most people to realize that they do not have to go downtown as they can work from home.

Current thinking is pushing a new “link” between Ottawa and Gatineau, with yet more expensive and disruptive infrastructure projects being touted, including a tramway or another tunnel under the downtown core.

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Ecology

That was then: Biggest earthquake since 1653 rocked Ottawa in 1925

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A regular weekly look-back at some offbeat or interesting stories that have appeared in the Ottawa Citizen over its 175-year history. Today: The big one hits.

The Ottawa Senators were playing a Saturday night game against the Montreal Canadiens at the Auditorium, the score tied 0-0 halfway through the second period. Sens’ rookie Ed Gorman and the Habs’ Billy Boucher had just served penalties for a dustup when the building began to make “ominous creaking sounds.” A window crashed to the ground.

Nearby, at Lisgar Collegiate, all eyes were on teenager Roxie Carrier, in the role of Donna Cyrilla in the musical comedy El Bandido. She had the stage to herself and was singing “Sometime” when the building rocked, the spotlight went out, and someone in the audience yelled “Fire!”

At a home on Carey Avenue, one woman’s normally relaxed cat suddenly arched its back, rushed around the room two or three times, spitting angrily, and climbed up the front-window curtains.

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Ecology

Ottawa delays small nuclear reactor plan as critics decry push for new reactors

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TORONTO — Canadians will have to wait a little while longer to see the federal government’s plan for the development of small nuclear reactors, seen by proponents as critical to the country’s fight against global warming.

Speaking at the opening of a two-day virtual international conference on Wednesday, the parliamentary secretary to the minister of natural resources said the plan will lay out key actions regarding the reactors. Its launch, Paul Lefebvre said, would come in the next few weeks.

“We’re still putting the finishing touches on it,” Lefebvre said. “The action plan is too important to be rushed.”

Small modular reactors — SMRs — are smaller in size and energy output than traditional nuclear power units, and more flexible in their deployment. While conventional reactors produce around 800 megawatts of power, SMRs can deliver up to 300 megawatts.

Proponents consider them ideal as both part of the regular electricity grid as well as for use in remote locations, including industrial sites and isolated northern communities. They could also play a role in the production of hydrogen and local heating.

“SMRs will allow us to take a bold step of meeting our goal of net-zero (emissions) by 2050 while creating good, middle class jobs and strengthening our competitive advantage,” said Lefebvre.

Natural Resources Minister Seamus O’Regan had been scheduled to speak at the conference but did not due to a family emergency.

Industry critics were quick to pounce on the government’s expected SMR announcement. They called on Ottawa to halt its plans to fund the experimental technology.

While nuclear power generation produces no greenhouse gas emissions, a major problem facing the industry is its growing mound of radioactive waste. This week, the government embarked on a round of consultations about what do with the dangerous material.

Dozens of groups, including the NDP, Bloc Quebecois, Green Party and some Indigenous organizations, oppose the plan for developing small modular reactors. They want the government to fight climate change by investing more in renewable energy and energy efficiency.

“We have options that are cheaper and safer and will be available quicker,” Richard Cannings, the NDP natural resources critic, said in a statement.

Lefebvre, however, said the global market for SMRs is expected to be worth between $150 billion and $300 billion a year by 2040. As one of the world’s largest producers of uranium, Canada has to be part of the wave both for economic and environmental reasons, he said.

“There’s a growing demand for smaller, simpler and affordable nuclear technology energy,” Lefebvre said.

Joe McBrearty, head of Canadian Nuclear Laboratories, told the conference the company had signed a host agreement this week with Ottawa-based Global First Power for a demonstration SMR at its Chalk River campus in eastern Ontario. A demonstration reactor will allow for the assessment of the technology’s overall viability, he said.

“When talking about deploying a new technology like an SMR, building a demonstration unit is vital to the success of that process,” McBrearty said. “Most importantly, it allows the public to see the reactor, to kick the tires so to speak, and to have confidence in the safety of its operation.”

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