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White Dwarfs + Compact Objects – Trottier Institute for Research on Exoplanets

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Our Institute’s researchers study more than just exoplanets. In addition to planets and the stars they orbit, our scientists also look at “dead” stars. Sometimes called compact objects or stellar remnants, these are the objects leftover at the end of a star’s life, once it has used up all of its fuel.

Death of a star

The most common type of stellar remnant is a white dwarf, the final fate of more than 97% of the stars in our Galaxy. White dwarfs are created when a small-to-moderately-large sized star burns all of its nuclear fusion fuel, and its core contracts. The outer layers are blown away to create a beautiful planetary nebula, revealing the dense core which has become a white dwarf. Imagine an object with mass similar to our Sun, but compressed down to the size of the Earth. A teaspoon of white dwarf material would weigh as much as three African elephants! This will be the ultimate fate of our own star, the Sun.

An artist’s rendering of an exoplanet orbiting the pulsar PSR B1257+12. (Credit: NASA/JPL-Caltech)

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Neutron stars are even more extreme stellar remnants. They are formed when very large stars run out of fuel. The process begins the same way as for white dwarfs, but in this case, there is too much mass and the contracting core squeezes past the white dwarf stage. The core squeezes down into a ball of pure neutrons.  They can have several times the mass of our Sun, but are only about as large as a city. These are the densest objects we know of, and a small handful of neutron star material on Earth would weigh as much as a mountain!

For the most massive stars, the collapse crushes even the ultra-dense ball of neutrons. These huge stars can turn into black holes when they exhaust their fuel. Black holes are extreme objects that have so much matter packed into such a tiny space that not even light goes fast enough to escape if it wanders too close.

Planets around dead stars?

What do these compact objects have to do with exoplanets? Since stellar remnants were once stars, they may have had planetary systems. They may have even retained their planets after their deaths. In fact, the first exoplanets ever discovered were not found around a regular star, but rather around a neutron star.

There is a special category of neutron stars called pulsars. They get this name because they rotate and pulse radio waves with incredible regularity, making pulsars some of the most stable clocks in the Universe. This regular pulse pattern can wobble slightly if other objects orbit the pulsar.  It was exactly this kind of pulsar wobble that revealed the very first confirmed exoplanet in 1992 around the pulsar PSR 1257+12. This discovery was made by Canadian astronomer Dale Frail (DRAO) and Polish astronomer Aleksander Wolszczan.

Polluted white dwarfs

An artist’s rendering of a destroyed comet around the white dwarf G29-38. (Credit: NASA/JPL-Caltech/GSFC)

White dwarfs provide a very different way of studying exoplanets. One important way that white dwarfs are different from regular stars is their high surface gravity. The gravity on the surface of a white dwarf would make a human weigh millions of kilograms! This causes heavier elements to sink rapidly, leaving a very clean and pure surface of mostly hydrogen and helium. As astronomers studied more white dwarfs, they discovered that some are “polluted” with heavier elements. The only way these heavy elements could be at the surface is if they were recently or continuously deposited there.

How could white dwarfs get polluted atmospheres? As a regular star nears the end of its life and eventually turns into a white dwarf, it can cause gravitational instabilities in its system. Objects such as planets, asteroids, and comets that may have been on stable orbits before the star died might now become unstable. If one of them falls too close to the white dwarf, it can easily be torn apart and form a disc of material that gets accreted onto the surface. Such polluted white dwarfs show us what these shredded objects were made of. This is different from measuring the composition of an exoplanet’s atmosphere, because polluted white dwarfs also reveal the planet’s crust and core materials, not just the atmospheric gasses.

No planets are yet known to exist around black holes, but that doesn’t mean it’s not possible. Researchers are currently looking for signs of planets in systems called x-ray binaries, where a black hole feeds off a stellar companion and emits strong x-rays.

White dwarfs and compact objects at iREx

Many of our iREx researchers are experts on these stellar remnants. Their expertise in these strange objects helps us to study exoplanets in unique ways. To learn more, we invite you to read their profiles:

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SpaceX launch marks 300th successful booster landing – Phys.org

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Credit: Unsplash/CC0 Public Domain

SpaceX sent up the 30th launch from the Space Coast for the year on the evening of April 23, a mission that also featured the company’s 300th successful booster recovery.

A Falcon 9 rocket carrying 23 of SpaceX’s Starlink internet satellites blasted off at 6:17 p.m. Eastern time from Cape Canaveral Space Force Station’s Space Launch Complex 40.

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The first-stage booster set a milestone of the 300th time a Falcon 9 or Falcon Heavy booster made a successful recovery landing, and the 270th time SpaceX has reflown a booster.

This particular booster made its ninth trip to space, a resume that includes one human spaceflight, Crew-6. It made its latest recovery landing downrange on the droneship Just Read the Instructions in the Atlantic Ocean.

The company’s first successful booster recovery came in December 2015, and it has not had a failed booster landing since February 2021.

The current record holder for flights flew 11 days ago making its 20th trip off the .

SpaceX has been responsible for all but two of the launches this year from either Kennedy Space Center or Cape Canaveral with United Launch Alliance having launched the other two.

SpaceX could knock out more launches before the end of the month, putting the Space Coast on pace to hit more than 90 by the end of the year, but the rate of launches by SpaceX is also set to pick up for the remainder of the year with some turnaround times at the Cape’s SLC-40 coming in less than three days.

That could amp up frequency so the Space Coast could surpass 100 launches before the end of the year, with the majority coming from SpaceX. It hosted 72 launches in 2023.

More launches from ULA are on tap as well, though, including the May 6 launch atop an Atlas V rocket of the Boeing CST-100 Starliner with a pair of NASA astronauts to the International Space Station.

ULA is also preparing for the second launch ever of its new Vulcan Centaur rocket, which recently received its second Blue Origin BE-4 engine and is just waiting on the payload, Sierra Space’s Dream Chaser spacecraft, to make its way to the Space Coast.

Blue Origin has its own it wants to launch this year as well, with New Glenn making its debut as early as September, according to SLD 45’s range manifest.

2024 Orlando Sentinel. Distributed by Tribune Content Agency, LLC.

Citation:
SpaceX launch marks 300th successful booster landing (2024, April 24)
retrieved 24 April 2024
from https://phys.org/news/2024-04-spacex-300th-successful-booster.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
part may be reproduced without the written permission. The content is provided for information purposes only.

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Wildlife Wednesday: loons are suffering as water clarity diminishes – Canadian Geographic

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The common loon, that icon of northern wilderness, is under threat from climate change due to declining water clarity. Published earlier this month in the journal Ecology, a study conducted by biologists from Chapman University and Rensselaer Polytechnic Institute in the U.S. has demonstrated the first clear evidence of an effect of climate change on this species whose distinct call is so tied to the soundscape of Canada’s lakes and wetlands.

Through the course of their research, the scientists found that July rainfall results in reduced July water clarify in loon territories in Northern Wisconsin. In turn, this makes it difficult for adult loons to find and capture their prey — mainly small fish — underwater, meaning they are unable to meet their chicks’ metabolic needs. Undernourished, the chicks face higher mortality rates. The consistent foraging techniques used by loons across their range means this impact is likely echoed wherever they are found — from Alaska to Canada to Iceland.

The researchers used Landsat imagery to find that there has been a 25-year consistent decline in water clarity, and during this period, body weights of adult loon and chicks alike have also declined. With July being the month of most rapid growth in young loons, the study also pinpointed water clarity in July as being the greatest predictor of loon body weight. 

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One explanation for why heavier rainfall leads to reduced water clarity is the rain might carry dissolved organic matter into lakes from adjacent streams and shoreline areas. Lawn fertilizers, pet waste and septic system leaks may also be to blame.

The researchers, led by Chapman University professor Walter Piper, hope to use these insights to further conservation efforts for this bird Piper describes as both “so beloved and so poorly understood.”

Return of the king

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Giant prehistoric salmon had tusk-like teeth for defence, building nests

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The artwork and publicity materials showcasing a giant salmon that lived five million years ago were ready to go to promote a new exhibit, when the discovery of two fossilized skulls immediately changed what researchers knew about the fish.

Initial fossil discoveries of the 2.7-metre-long salmon in Oregon in the 1970s were incomplete and had led researchers to mistakenly suggest the fish had fang-like teeth.

It was dubbed the “sabre-toothed salmon” and became a kind of mascot for the Museum of Natural and Cultural History at the University of Oregon, says researcher Edward Davis.

But then came discovery of two skulls in 2014.

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Davis, a member of the team that found the skulls, says it wasn’t until they got back to the lab that he realized the significance of the discovery that has led to the renaming of the fish in a new, peer-reviewed study.

“There were these two skulls staring at me with sideways teeth,” says Davis, an associate professor in the department of earth sciences at the university.

In that position, the tusk-like teeth could not have been used for biting, he says.

“That was definitely a surprising moment,” says Davis, who serves as director of the Condon Fossil Collection at the university’s Museum of Natural and Cultural History.

“I realized that all of the artwork and all of the publicity materials and bumper stickers and buttons and T-shirts we had just made two months prior, for the new exhibit, were all out of date,” he says with a laugh.

Davis is co-author of the new study in the journal PLOS One, which renames the giant fish the “spike-toothed salmon.”

It says the salmon used the tusk-like spikes for building nests to spawn, and as defence mechanisms against predators and other salmon.

The salmon lived about five million years ago at a time when Earth was transitioning from warmer to relatively cooler conditions, Davis says.

It’s hard to know exactly why the relatives of today’s sockeye went extinct, but Davis says the cooler conditions would have affected the productivity of the Pacific Ocean and the amount of rain feeding rivers that served as their spawning areas.

Another co-author, Brian Sidlauskas, says a fish the size of the spike-toothed salmon must have been targeted by predators such as killer whales or sharks.

“I like to think … it’s almost like a sledgehammer, these salmon swinging their head back and forth in order to fend off things that might want to feast on them,” he says.

Sidlauskas says analysis by the lead author of the paper, Kerin Claeson, found both male and female salmon had the “multi-functional” spike-tooth feature.

“That’s part of our reason for hypothesizing that this tooth is multi-functional … It could easily be for digging out nests,” he says.

“Think about how big the (nest) would have to be for an animal of this size, and then carving it out in what’s probably pretty shallow water; and so having an extra digging tool attached to your head could be really useful.”

Sidlauskas says the giant salmon help researchers understand the boundaries of what’s possible with the evolution of salmon, but they also capture the human imagination and a sense of wonder about what’s possible on Earth.

“I think it helps us value a little more what we do still have, or I hope that it does. That animal is no longer with us, but it is a product of the same biosphere that sustains us.”

This report by The Canadian Press was first published April 24, 2024.

Brenna Owen, The Canadian Press

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