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Invisible matter matters – The Varsity – Varsity

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ARTHUR DENNYSON HAMDANI/THEVARSITY

Theories of galaxy formation and dark matter

A galaxy is a huge collection of stars, dust, and gas held together by gravity and moving through space together. Our solar system, like many others, orbits around the center of a galaxy — in our case, the Milky Way. 

So, how did this happen? Why do solar systems exist in these structures rather than in isolation? In other words, what forms galaxies? 

Theories of galaxy formation

Astrophysicists are still researching galaxy formation to this day. Some theories posit that following the Big Bang — the theory that the universe started and expanded from a single intensely dense point — gravity pulled matter to create dense clumps that grouped together. The clumps that did not dissipate because  other opposing forces grew larger, attracting more matter around them. 

Eventually, high amounts of the clumped matter collapsed under their own gravity. These clumps formed within the first few hundred thousand years of the universe’s existence, developing into the first proto-galaxies that we see today. 

A 1962 paper by astrophysicists O. J. Eggen, D. Lynden-Bell, and A. R. Sandage suggested that the mass of proto-galaxies was comparable to the mass of today’s galaxies. At this size, the clumps of matter collapse under their own gravity and become proto-galaxies, which later develop into mature galaxies. This is known as the top-down or Monolithic Collapse model.

However, in 1984, physicists J. R. Primack, G. Blumenthal, and S. M. Fabera proposed the Lambda Cold Dark Matter model, which builds on a bottom-up model that opposes the top-down model. It instead states that proto-galaxies grew into mature galaxies through galactic mergers or the collision of two or more galaxies. The Lambda Cold Dark Matter model adds cold — or slow-moving — dark matter to the equation of galaxy formation. Dark matter is an invisible form of matter that does not interact with light. It does, however, have gravitational effects on galaxies and galaxy clusters. It is through its gravitational influence, then, that astrophysicists measure dark matter and why they think dark matter exists. 

The Lambda Cold Dark Matter model explains the initial clumping of matter after the Big Bang, arguing that the pronounced variations in dark matter density throughout the universe initially clumped together and collapsed under their own gravity, attracting visible matter to form visible proto-galaxies. The model then continues with the bottom-up model of proto-galaxy maturation through galactic mergers. 

Physicists prefer this model, and it is more supported by observational data, such as evidence of mergers that astronomers can observe by viewing distant galaxies in the process of merging, dwarf galaxies near larger galaxies that are at the beginning of merging, or even faint tails of gas associated with galaxies that are left-over indications of past mergers. 

But if dark matter is invisible, how can physicists even study it to develop a model that includes it in galaxy formation?

Dark matter 

Dark matter accounts for around 85 per cent of the total matter in the universe or over five times more than visible matter. 

Each galaxy has its own ‘halo’ of dark matter around it that has more mass than all the other matter in that galaxy put together. This dark matter halo influences the movement of that galaxy. Furthermore, the gravitational interactions of the halos of different galaxies contribute to driving the growth and structure of galaxies. 

The existence of this halo of dark matter can be seen through an effect called gravitational lensing. Massive objects bend space-time, the fabric of the universe, and that warp also causes light to bend around sources of high mass. This causes distortion and magnification of light from objects behind and in the same line of sight as the mass, causing space-time bending. 

Galaxies bend space-time and cause the distortion and magnification of light from other galaxies further back. Physicists use this level of distortion to calculate the amount of mass in a galaxy or a cluster of galaxies, as well as its location. Astrophysicists concluded that dark matter must exist to account for the mass required to cause these distortions. 

The Chandra X-Ray Observatory obtained evidence for dark matter by studying a particular cluster of galaxies called the Bullet cluster

A previous high-energy collision between two large galaxies formed the Bullet cluster around 3.8 billion light years away from Earth. Because dark matter does not directly interact with itself or with other matter like gas, it was not impacted in the collision, whereas other visible matter like gas was. This caused a separation between dark matter and visible matter in the cluster. Optical imaging of the cluster shows this separation of mass and how nearly all the matter in the cluster is dark matter. This separation of matter allows us to avoid conflating dark matter and visible matter – it allows us to understand that dark matter is a separate type of matter from visible matter. 

So, galaxies and how they behave and form largely depend on dark matter interactions, and there is still a lot more to learn about them. Astrophysicists worldwide are still intensely researching questions like what dark matter is made of, what causes supermassive black holes in the middle of galaxies, and many more. In fact, the Dunlap Institute for Astronomy and Astrophysics at U of T is one of the research facilities studying these topics and the many questions they raise.

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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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