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How stars can help us find dark matter

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Professor Ting Li explains how stellar streams can help us elucidate mass distribution in the Milky Way. COURTESY OF ASX ASSOCIATION

Astronomers hunt for dark matter through ribbon-like remnants of dead galaxies

On the morning of November 24, Assistant Professor Ting Li at U of T’s Department of Astronomy and Astrophysics was awarded the 2023 Dorothy Shoichet Women Faculty in Science Award of Excellence. Later that evening, she gave a Star Talk, a series hosted by U of T’s Astronomy & Space Exploration Association, titled “Navigating Stellar Streams: Unveiling the Milky Way’s Hidden Secrets.”

I was nervous being in that lecture hall. I hadn’t been to an astrophysics lecture in six years. Luckily, the talk was approachable to those without a physics background.

Seeing dark matter in the Milky Way

Large images and graphs accompanied Li’s talk. One was a simulated density map of dark matter in the Milky Way, which is a spiral galaxy, or a massive collection of stars, dust, and gas in the form of a spinning pinwheel. In general, density maps are maps of a region in the sky where lighter areas of the region indicate high clusters, or a high density of whatever matter scientists are measuring, and darker areas indicate sparser matter in a given region.

Dark matter, according to NASA, is an unknown matter that makes up about 27 per cent of our universe and is not visible or normal matter. Dark matter has mass that can bend the light travelling from galaxies behind it. The degree to which this mass bends the light helps astronomers create density maps of dark matter.

On the other hand, a stellar density map of the Milky Way — where Earth resides — is a density map that would help configure the distribution of stars in the galaxy as well as the structure of our galaxy’s swirling arms.

And these density maps show a lot. Surrounding the disc of the Milky Way is a gigantic spherical halo shape of dark matter known as the main halo, and it is orbited by many smaller and more compact clusters of dark matter known as sub-halos. Sub-halos that are large enough and have enough gas can create stars and dwarf galaxies smaller than the Milky Way.

Dwarf galaxies like the Large and Small Magellanic Clouds can orbit the Milky Way as satellite galaxies. Satellite galaxies are essentially galaxies that orbit other galaxies, like planets orbiting the Sun.

If satellite galaxies get too close to the Milky Way, they can end up as ribbon-like structures called stellar streams. These streams are the remains of galaxies and star clusters that have been ripped apart due to the Milky Way’s gravitational pull and now exist as linear clusters of individual stars, called member stars.

Stellar streams and how to find them

The importance of stellar streams lies in their ability to answer questions about the mass and shape of the Milky Way. Stellar streams can help in understanding how much dark matter mass is in our galaxy and how it affects the Milky Way.

While nearly a third of the universe is made up of dark matter, most of the Milky Way is dark matter. Finding dark matter would help us understand the weight of the galaxy and that in turn would help answer cosmological questions, especially about the evolution of galaxies.

Li used the analogy of Christmas lights to demonstrate the role of stellar streams. Just like the shape of Christmas lights on a tree in the dark can provide an idea of what the tree looks like, stellar streams function as visible matter that can help us infer the mass distribution of the Milky Way.

Astronomers are using sky surveys to discover stellar streams. Using powerful cameras, they image the sky multiple times to look for data on stars, like their brightness and location. Stellar density maps, created by powerful cameras, are used to map member stars and then detect stellar streams.

Astronomers have known of the existence of stellar streams since 1994, and research on stellar streams has been rising dramatically for the last two decades due to emerging surveys. One reason for this sharp increase in discoveries is the advancement of giant telescopic cameras with diameters at least a metre wide. The specific camera Li mentioned was the Dark Energy Camera, part of a four-metre telescope located at the Cerro Tololo Inter-American Observatory in Chile.

Space satellites like Gaia and the Giant Magellan Telescope have also helped pave the way to discovering more stellar streams. Gaia is a spacecraft with the main mission to create a precise 3D map of more than a thousand million stars in our galaxy and beyond. According to the Smithsonian Astrophysical Observatory, the Giant Magellan Telescope is going to be the world’s largest and most powerful telescope and is to be operational by 2029.

The takeaway

I realized I had been leaning over the desk for the entire lecture. I stuck around to sit down with Professor Li, who told me that there is beauty in discovering something you never meant to.

Awe had replaced my nerves by then. I had stumbled upon a whole world I didn’t know about, which included discoveries, people, and entire entities that are much more than meets the eye.

 

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Here’s how Helene and other storms dumped a whopping 40 trillion gallons of rain on the South

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More than 40 trillion gallons of rain drenched the Southeast United States in the last week from Hurricane Helene and a run-of-the-mill rainstorm that sloshed in ahead of it — an unheard of amount of water that has stunned experts.

That’s enough to fill the Dallas Cowboys’ stadium 51,000 times, or Lake Tahoe just once. If it was concentrated just on the state of North Carolina that much water would be 3.5 feet deep (more than 1 meter). It’s enough to fill more than 60 million Olympic-size swimming pools.

“That’s an astronomical amount of precipitation,” said Ed Clark, head of the National Oceanic and Atmospheric Administration’s National Water Center in Tuscaloosa, Alabama. “I have not seen something in my 25 years of working at the weather service that is this geographically large of an extent and the sheer volume of water that fell from the sky.”

The flood damage from the rain is apocalyptic, meteorologists said. More than 100 people are dead, according to officials.

Private meteorologist Ryan Maue, a former NOAA chief scientist, calculated the amount of rain, using precipitation measurements made in 2.5-mile-by-2.5 mile grids as measured by satellites and ground observations. He came up with 40 trillion gallons through Sunday for the eastern United States, with 20 trillion gallons of that hitting just Georgia, Tennessee, the Carolinas and Florida from Hurricane Helene.

Clark did the calculations independently and said the 40 trillion gallon figure (151 trillion liters) is about right and, if anything, conservative. Maue said maybe 1 to 2 trillion more gallons of rain had fallen, much if it in Virginia, since his calculations.

Clark, who spends much of his work on issues of shrinking western water supplies, said to put the amount of rain in perspective, it’s more than twice the combined amount of water stored by two key Colorado River basin reservoirs: Lake Powell and Lake Mead.

Several meteorologists said this was a combination of two, maybe three storm systems. Before Helene struck, rain had fallen heavily for days because a low pressure system had “cut off” from the jet stream — which moves weather systems along west to east — and stalled over the Southeast. That funneled plenty of warm water from the Gulf of Mexico. And a storm that fell just short of named status parked along North Carolina’s Atlantic coast, dumping as much as 20 inches of rain, said North Carolina state climatologist Kathie Dello.

Then add Helene, one of the largest storms in the last couple decades and one that held plenty of rain because it was young and moved fast before it hit the Appalachians, said University of Albany hurricane expert Kristen Corbosiero.

“It was not just a perfect storm, but it was a combination of multiple storms that that led to the enormous amount of rain,” Maue said. “That collected at high elevation, we’re talking 3,000 to 6000 feet. And when you drop trillions of gallons on a mountain, that has to go down.”

The fact that these storms hit the mountains made everything worse, and not just because of runoff. The interaction between the mountains and the storm systems wrings more moisture out of the air, Clark, Maue and Corbosiero said.

North Carolina weather officials said their top measurement total was 31.33 inches in the tiny town of Busick. Mount Mitchell also got more than 2 feet of rainfall.

Before 2017’s Hurricane Harvey, “I said to our colleagues, you know, I never thought in my career that we would measure rainfall in feet,” Clark said. “And after Harvey, Florence, the more isolated events in eastern Kentucky, portions of South Dakota. We’re seeing events year in and year out where we are measuring rainfall in feet.”

Storms are getting wetter as the climate change s, said Corbosiero and Dello. A basic law of physics says the air holds nearly 4% more moisture for every degree Fahrenheit warmer (7% for every degree Celsius) and the world has warmed more than 2 degrees (1.2 degrees Celsius) since pre-industrial times.

Corbosiero said meteorologists are vigorously debating how much of Helene is due to worsening climate change and how much is random.

For Dello, the “fingerprints of climate change” were clear.

“We’ve seen tropical storm impacts in western North Carolina. But these storms are wetter and these storms are warmer. And there would have been a time when a tropical storm would have been heading toward North Carolina and would have caused some rain and some damage, but not apocalyptic destruction. ”

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Follow AP’s climate coverage at https://apnews.com/hub/climate

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Follow Seth Borenstein on Twitter at @borenbears

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Associated Press climate and environmental coverage receives support from several private foundations. See more about AP’s climate initiative here. The AP is solely responsible for all content.

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‘Big Sam’: Paleontologists unearth giant skull of Pachyrhinosaurus in Alberta

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It’s a dinosaur that roamed Alberta’s badlands more than 70 million years ago, sporting a big, bumpy, bony head the size of a baby elephant.

On Wednesday, paleontologists near Grande Prairie pulled its 272-kilogram skull from the ground.

They call it “Big Sam.”

The adult Pachyrhinosaurus is the second plant-eating dinosaur to be unearthed from a dense bonebed belonging to a herd that died together on the edge of a valley that now sits 450 kilometres northwest of Edmonton.

It didn’t die alone.

“We have hundreds of juvenile bones in the bonebed, so we know that there are many babies and some adults among all of the big adults,” Emily Bamforth, a paleontologist with the nearby Philip J. Currie Dinosaur Museum, said in an interview on the way to the dig site.

She described the horned Pachyrhinosaurus as “the smaller, older cousin of the triceratops.”

“This species of dinosaur is endemic to the Grand Prairie area, so it’s found here and nowhere else in the world. They are … kind of about the size of an Indian elephant and a rhino,” she added.

The head alone, she said, is about the size of a baby elephant.

The discovery was a long time coming.

The bonebed was first discovered by a high school teacher out for a walk about 50 years ago. It took the teacher a decade to get anyone from southern Alberta to come to take a look.

“At the time, sort of in the ’70s and ’80s, paleontology in northern Alberta was virtually unknown,” said Bamforth.

When paleontogists eventually got to the site, Bamforth said, they learned “it’s actually one of the densest dinosaur bonebeds in North America.”

“It contains about 100 to 300 bones per square metre,” she said.

Paleontologists have been at the site sporadically ever since, combing through bones belonging to turtles, dinosaurs and lizards. Sixteen years ago, they discovered a large skull of an approximately 30-year-old Pachyrhinosaurus, which is now at the museum.

About a year ago, they found the second adult: Big Sam.

Bamforth said both dinosaurs are believed to have been the elders in the herd.

“Their distinguishing feature is that, instead of having a horn on their nose like a triceratops, they had this big, bony bump called a boss. And they have big, bony bumps over their eyes as well,” she said.

“It makes them look a little strange. It’s the one dinosaur that if you find it, it’s the only possible thing it can be.”

The genders of the two adults are unknown.

Bamforth said the extraction was difficult because Big Sam was intertwined in a cluster of about 300 other bones.

The skull was found upside down, “as if the animal was lying on its back,” but was well preserved, she said.

She said the excavation process involved putting plaster on the skull and wooden planks around if for stability. From there, it was lifted out — very carefully — with a crane, and was to be shipped on a trolley to the museum for study.

“I have extracted skulls in the past. This is probably the biggest one I’ve ever done though,” said Bamforth.

“It’s pretty exciting.”

This report by The Canadian Press was first published Sept. 25, 2024.

The Canadian Press. All rights reserved.

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The ancient jar smashed by a 4-year-old is back on display at an Israeli museum after repair

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TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.

Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.

Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.

The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.

The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.

It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.

Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.

Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.

Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.

Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.

Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.

The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”

The Canadian Press. All rights reserved.

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