‘Dark matter caused mass extinctions, geologic upheavals’
Guides growth of supermassive black holes
With new data, Planck satellite brings early universe into focus
WAS dark matter responsible for mass extinctions, geologic upheavals, which killed of the dinosaurs? Has football-shaped collections of stars called elliptical galaxies provided new insights into the connection between a galaxy and its black hole? Has the Planck space telescope offered a glimpse of what the universe looked like almost 14 billion years ago, when it was just 380,000 years old?
Three separate but independent studies might have provided answers to these questions.
Research by New York University, United States, Biology Professor Michael Rampino concludes that Earth’s infrequent but predictable path around and through our Galaxy’s disc may have a direct and significant effect on geological and biological phenomena occurring on Earth.
In a new paper in Monthly Notices of the Royal Astronomical Society, he concludes that movement through dark matter may perturb the orbits of comets and lead to additional heating in Earth’s core, both of which could be connected with mass extinction events.
According to Wikipedia, dark matter is a hypothetical kind of matter that cannot be seen with telescopes but accounts for most of the matter in the Universe. The existence and properties of dark matter are inferred from its gravitational effects on visible matter, radiation, and the large-scale structure of the Universe. It has not been detected directly, making it one of the greatest mysteries in modern astrophysics.
An extinction (level) event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the amount of life on Earth.
The Galactic disc is the region of the Milky Way Galaxy where our solar system resides. It is crowded with stars and clouds of gas and dust, and also a concentration of elusive dark matter — small subatomic particles that can be detected only by their gravitational effects.
Previous studies have shown that Earth rotates around the disc-shaped Galaxy once every 250 million years.
But Earth’s path around the Galaxy is wavy, with the Sun and planets weaving through the crowded disc approximately every 30 million years. Analyzing the pattern of Earth’s passes through the Galactic disc, Rampino notes that these disc passages seem to correlate with times of comet impacts and mass extinctions of life. The famous comet strike 66 million ago that led to the extinction of the dinosaurs is just one example.
What causes this correlation between Earth’s passes through the Galactic disc, and the impacts and extinctions that seem to follow?
While traveling through the disc, the dark matter concentrated there disturbs the pathways of comets typically orbiting far from Earth in the outer Solar System, Rampino observes. This means that comets that would normally travel at great distances from Earth instead take unusual paths, causing some of them to collide with the planet.
But even more remarkably, with each dip through the disc, the dark matter can apparently accumulate within Earth’s core. Eventually, the dark matter particles annihilate each other, producing considerable heat. The heat created by the annihilation of dark matter in Earth’s core could trigger events such as volcanic eruptions, mountain building, magnetic field reversals, and changes in sea level, which also show peaks every 30 million years. Rampino therefore suggests that astrophysical phenomena derived from Earth’s winding path through the Galactic disc, and the consequent accumulation of dark matter in the planet’s interior, can result in dramatic changes in Earth’s geological and biological activity.
His model of dark matter interactions with Earth as it cycles through the Galaxy could have a broad impact on our understanding of the geological and biological development of Earth, as well as other planets within the Galaxy.
Rampino said: “We are fortunate enough to live on a planet that is ideal for the development of complex life. But the history of Earth is punctuated by large scale extinction events, some of which we struggle to explain. It may be that dark matter — the nature of which is still unclear but which makes up around a quarter of the universe — holds the answer. As well as being important on the largest scales, dark matter may have a direct influence on life on Earth.”
In the future, he suggests, geologists might incorporate these astrophysical findings in order to better understand events that are now thought to result purely from causes inherent to Earth. This model, Rampino adds, likewise provides new knowledge of the possible distribution and behavior of dark matter within the
Meanwhile, a new study of football-shaped collections of stars called elliptical galaxies provides new insights into the connection between a galaxy and its black hole. It finds that the invisible hand of dark matter somehow influences black hole growth.
Every massive galaxy has a black hole at its center, and the heftier the galaxy, the bigger its black hole. But why are the two related? After all, the black hole is millions of times smaller and less massive than its home galaxy.
“There seems to be a mysterious link between the amount of dark matter a galaxy holds and the size of its central black hole, even though the two operate on vastly different scales,” says lead author Akos Bogdan of the Harvard-Smithsonian Center for Astrophysics (CfA).
This new research was designed to address a controversy in the field. Previous observations had found a relationship between the mass of the central black hole and the total mass of stars in elliptical galaxies. However, more recent studies have suggested a tight correlation between the masses of the black hole and the galaxy’s dark matter halo. It wasn’t clear which relationship dominated.
In our universe, dark matter outweighs normal matter — the everyday stuff we see all around us — by a factor of six to one. We know dark matter exists only from its gravitational effects. It holds together galaxies and galaxy clusters. Every galaxy is surrounded by a halo of dark matter that weighs as much as a trillion suns and extends for hundreds of thousands of light-years.
To investigate the link between dark matter halos and supermassive black holes, Bogdan and his colleague Andy Goulding (Princeton University) studied more than 3,000 elliptical galaxies. They used star motions as a tracer to weigh the galaxies’ central black holes. X-ray measurements of hot gas surrounding the galaxies helped weigh the dark matter halo, because the more dark matter a galaxy has, the more hot gas it can hold onto.
They found a distinct relationship between the mass of the dark matter halo and the black hole mass — a relationship stronger than that between a black hole and the galaxy’s stars alone.
This connection is likely to be related to how elliptical galaxies grow. An elliptical galaxy is formed when smaller galaxies merge, their stars and dark matter mingling and mixing together. Because the dark matter outweighs everything else, it molds the newly formed elliptical galaxy and guides the growth of the central black hole.
“In effect, the act of merging creates a gravitational blueprint that the galaxy, the stars and the black hole will follow in order to build themselves,” explains Bogdan.
Meanwhile, from its orbit 930,000 miles above Earth, the Planck space telescope spent more than four years detecting the oldest light in the universe, called the cosmic microwave background. This fossil from the Big Bang fills every square inch of the sky and offers a glimpse of what the universe looked like almost 14 billion years ago, when it was just 380,000 years old.
Planck’s observations of this relic radiation shed light on everything from the evolution of the universe to dark matter. Just this month, Planck released new maps of the cosmic microwave background supporting the theory of cosmic inflation, which posits that the universe underwent a monumental expansion in the moments following the Big Bang. During this time, space expanded faster than the speed of light, growing from smaller than a proton to an enormity that defies comprehension.
Yet the theory of inflation is not yet a full and detailed theory that can completely explain the universe’s earliest moments. “We don’t yet understand the fundamental physics that drove inflation, and we certainly don’t understand the details of how it worked,” said George Efstathiou, director of the Kavli Institute for Cosmology at the University of Cambridge and one of the leaders of the Planck mission. Efstathiou offered his insights during a recent conversation with The Kavli Foundation. “What we need is better experimental data that tells us what the early universe looked like and hopefully this will point us toward a fundamental theory of inflation.”
That said, the latest Planck data do support the general idea that the universe expanded mindbogglingly fast in its first moments. The data also offers insight into neutrinos, the tiny, ubiquitous particles known come in three types but whose mass is still unknown. Previous experiments determined the lightest these particles could be; the Planck results have now set a limit on heaviest they could possibly be.
“We’re narrowing down the options, and will hopefully soon learn their exact mass,” said Efstathiou. “Neutrinos are some of the most mysterious particles in the universe, so this would be an important step toward understanding them.”
Planck also looked for dark matter — the mysterious substance that makes up 20 percent of the universe yet has yet to be well understood — but found no signal whatsoever. That’s not all that surprising, said Efstathiou. Dark matter is easy to hide, and it will take future experiments to find it. Theorists have also suggested that dark matter might interact in some way with dark energy, the substance that permeates all of space and pushes the universe apart. From the Planck data, Efstathiou said, it looks like dark energy is completely constant and does not interact with dark matter.
In addition, Efstathiou said that although no experiment has yet detected gravitational waves, ripples in the curvature of space-time that, if they exist, could help prove the theory of inflation, future experiments have a good shot at it.
“If you look at the [data], you see that there’s plenty of room for gravitational waves to be lurking there, just below the level” we can see, he said. “If that’s true, it shouldn’t take a very long time to dig it out. So there could be a very important development coming.”
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