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How Do Stars Get So Massive? Their Dense, Unstable Disks Could Be To Blame

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Gaia 17bpi star

This artist’s impression shows the inner disk of a young star collapsing onto its host, becoming hot enough to emit visible light. (Credit: Caltech/T. Pyle (IPAC))

Any bodybuilder will tell you that you can’t bulk up overnight, but that might not be true for stars. While observing infant star Gaia 17bpi, astronomers saw part of its dense disk collapse onto its body below — adding mass at an incredible rate. This encounter is one of the few times that researchers have seen a star’s disk become gravitationally unstable and fall down to its host. The findings, which will appear in the Astrophysical Journal, could shed light on stellar evolution and help answer the ever-looming question: how do stars become so massive?

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Astronomers have a pretty solid understanding of star formation and evolution: a cold, dense cloud of dust and gas collapses under its own gravity and condenses into a hot ball of matter. The remaining dust and gas form a swirling disk around the infant star, from which it slowly but continually steals material from. Previous observations, though, show that the rate stars steal from their disks is too slow to result in their final, enormous masses.

Luckily, one classification of stars could help explain how they gain their mysterious, unaccounted mass. Called FU Ori’s, this class represents stars that are only a few million years old and are surrounded by thick disks of dust and gas. As these disks grow, they become so massive that they lose gravitational stability, and end up dumping their heavy, dusty loads onto their host stars. It’s believed that all stars undergo 10 to 20 of these FU Ori events in their early years, but since they’re still hidden behind the molecular clouds that they formed in, they can be difficult to detect.

Tracking Trio

But thanks to data from three high-tech instruments, a team led by California Institute of Technology (Caltech) astronomers was able to capture one of these rare events. The discovery started when ESA’s Gaia mission, which is tasked with mapping a billion nearby stars, spotted a star that was increasing in brightness. Intrigued, the team followed up and found that NASA’s NEOWISE satellite, which scans the skies for asteroids and comets, and their Spitzer Space Telescope witnessed the event, too.

Capable to detecting infrared wavelengths, data from both NEOWISE and Spitzer showed that dust and gas in the star’s disk started to build up and become hotter, causing it to emit beams of infrared light. It’s believed that part of the disk grew so dense that it collapsed under its own gravity and fell toward its host star, dubbed Gaia 17bpi. And when it did, the matter grew hot enough to emit the influx of visible light detected by Gaia.

“These FU Ori events are extremely important in our current understanding of the process of star formation but have remained almost mythical because they have been so difficult to observe,” said Lynne Hillenbrand, a Caltech astronomy professor and lead author of the paper, in a media release. “This is actually the first time we’ve ever seen one of these events as it happens in both optical and infrared light, and these data have let us map the movement of material through the disk and onto the star.”

Added to the list of just 25 FU Ori’s ever detected, Gaia 17bpi’s sudden growth spurt could further solidify this stellar evolution theory, and help solve the mystery of massive stars once and for all.

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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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