Tag: cosmos

Universe’s First Stars Detected? Here Are The Facts!

Stars are our constant companions in the night sky, but seas of twinkling lights weren’t always a feature of the cosmos.

Now, scientists peering back into deep time suggest that the earliest stars didn’t turn on until about 180 million years after the big bang, when the universe as we know it exploded into existence.

For decades, teams of scientists have been chasing—in fact, racing—to detect the signatures of these first stars.

The new detection, from a project called EDGES, is in the form of a radio signal triggered when light from those stars began interacting with the hydrogen gas that filled primordial empty space.

If the signal stands up to scrutiny, the detection simultaneously opens up a new line of cosmological inquiry and offers a few conundrums to tackle.

The era of cosmic dawn has been entirely uncharted territory until now,” says physicist Cynthia Chiang of the University of KwaZulu-Natal in South Africa.

It’s extremely exciting to see a new glimpse of this slice of the universe’s history, and the EDGES detection is the initial step toward understanding the nature of the first stars in more detail.

Cosmic Dawn

Shortly after the universe was born, it was plunged into darkness. The first stars turned on when hot gas coalesced around clumps of dark matter, then contracted and became dense enough to ignite the nuclear hearts of infant suns.

As those early stars began breathing ultraviolet light into the cosmos, their photons mingled with primordial hydrogen gas, causing it to absorb background radiation and become translucent.

When that happened, those hydrogen atoms produced radio waves that traveled through space at a predictable frequency, which astronomers can still observe today with radio telescopes.

The same process is going on in modern stars as they continue to send light into the cosmos.

But the radio waves produced by those first stellar gasps have been traveling through space for so long that they’ve been stretched, or redshifted.

That’s how astronomers identified the fingerprints of the earliest stars in radio waves detected by a small antenna in western Australia.

From Light to Dark

If the signal is real, it presents a challenge for some scientists who’ve been thinking about how the early universe worked.

For starters, the time frame during which these earliest stars emerged lines up well with some theories, but it’s not exactly bang on with others.

In previous work, Furlanetto and his colleagues started with actual observations of the earliest known galaxies, and then rewound the cosmic clock using computer models, searching for the age at which a signal from the first stars might appear.

The universe’s first galaxies are thought to be small, fragile, and not that great at birthing stars, so Furlanetto wouldn’t expect the signal to peak until about 325 million years after the big bang.

But if the first stars had already furnished enough light to make their presence known 180 million years after the big bang, those early galaxies must be doing something different.

As well, the primordial hydrogen gas is absorbing photons at rates that are at least two times higher than predicted.

That’s problematic for some ideas about the temperature of the early universe. It means that either the primordial gas was colder than expected, or background radiation was hotter.

Dark matter makes up the bulk of the universe’s mass, but it doesn’t behave like normal matter and has proven tricky to understand.

It regularly evades direct detection, and scientists are struggling to pin down, what, exactly it is and how it has influenced the structure of the universe through time.

But, she notes, it’s way too early to accept that conclusion.

An alternate possibility is that there are simply more photons for the hydrogen gas to absorb, though it’s not obvious where all those photons would come from in the early universe.

So she and others are waiting for independent confirmation of the EDGES result before diving too deep into the possible dark matter scenarios.

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Pass it on: Popular Science

Why Can’t We Feel Earth’s Spin?

Earth spins on its axis once in every 24-hour day. At Earth’s equator, the speed of Earth’s spin is about 1,000 miles per hour (1,600 kph).

The day-night has carried you around in a grand circle under the stars every day of your life, and yet you don’t feel Earth spinning.

Why not? It’s because you and everything else – including Earth’s oceans and atmosphere – are spinning along with the Earth at the same constant speed.

It’s only if Earth stopped spinning, suddenly, that we’d feel it. Then it would be a feeling similar to riding along in a fast car, and having someone slam on the brakes!

Think about riding in a car or flying in a plane. As long as the ride is going smoothly, you can almost convince yourself you’re not moving.

A jumbo jet flies at about 500 miles per hour (about 800 km per hour), or about half as fast as the Earth spins at its equator. But, while you’re riding on that jet, if you close your eyes, you don’t feel like you’re moving at all.

And when the flight attendant comes by and pours coffee into your cup, the coffee doesn’t fly to the back of the plane. That’s because the coffee, the cup and you are all moving at the same rate as the plane.

Now think about what would happen if the car or plane wasn’t moving at a constant rate, but instead speeding up and slowing down. Then, when the flight attendant poured your coffee … look out!

Earth is moving at a fixed rate, and we’re all moving along with it, and that’s why we don’t feel Earth’s spin. If Earth’s spin were suddenly to speed up or slow down, you would definitely feel it.

The constant spin of the Earth had our ancestors pretty confused about the true nature of the cosmos. They noticed that the stars, and the sun and the moon, all appeared to move above the Earth.

Because they couldn’t feel Earth move, they logically interpreted this observation to mean that Earth was stationary and “the heavens” moved above us.

With the notable exception of the early Greek scientist Aristarchus, who first proposed a heliocentric model of the universe hundreds of years B.C.E., the world’s great thinkers upheld the geocentric idea of the cosmos for many centuries.

It wasn’t until the 16th Century that the heliocentric model of Copernicus began to be discussed and understood.

While not without errors, Copernicus’ model eventually convinced the world that Earth spun on its axis beneath the stars … and also moved in orbit around the sun.

Bottom line: Why don’t we feel Earth rotating, or spinning, on its axis? It’s because Earth spins steadily – and moves at a constant rate in orbit around the sun – carrying you as a passenger right along with it.

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Pass it on: Popular Science

Mysterious Dark Matter May Not Always Have Been Dark

The nature of dark matter is currently one of the greatest mysteries in science. The invisible substance — which is detectable via its gravitational influence on “normal” matter — is thought to make up five-sixths of all matter in the universe.

Astronomers began suspecting the existence of dark matter when they noticed the cosmos seemed to possess more mass than stars could account for.

For example, stars circle the center of the Milky Way so fast that they should overcome the gravitational pull of the galaxy’s core and zoom into the intergalactic void.

Most scientists think dark matter provides the gravity that helps hold these stars back.

Scientists have mostly ruled out all known ordinary materials as candidates for dark matter. The consensus so far is that this missing mass is made up of new species of particles that interact only very weakly with ordinary matter.

One potential clue about the nature of dark matte rhas to do with the fact that it’s five times more abundant than normal matter, researchers said.

This may seem a lot, and it is, but if dark and ordinary matter were generated in a completely independent way, then this number is puzzling,” said study co-author Pavlos Vranas, a particle physicist at Lawrence Livermore National Laboratory in Livermore, California.

Instead of five, it could have been a million or a billion. Why five?

The researchers suggest a possible solution to this puzzle: Dark matter particles once interacted often with normal matter, even though they barely do so now.

The protons and neutrons making up atomic nuclei are themselves each made up of a trio of particles known as quarks.

The researchers suggest dark matter is also made of a composite “stealth” particle, which is composed of a quartet of component particles and is difficult to detect.

The scientists’ supercomputer simulations suggest these composite particles may have masses ranging up to more than 200 billion electron-volts, which is about 213 times a proton’s mass.

Quarks each possess fractional electrical charges of positive or negative one-third or two-thirds. In protons, these add up to a positive charge, while in neutrons, the result is a neutral charge.

Quarks are confined within protons and neutrons by the so-called “strong interaction.

The researchers suggest that the component particles making up stealth dark matter particles each have a fractional charge of positive or negative one-half, held together by a “dark form” of the strong interaction.

Stealth dark matter particles themselves would only have a neutral charge, leading them to interact very weakly at best with ordinary matter, light, electric fields and magnetic fields.

The researchers suggest that at the extremely high temperatures seen in the newborn universe, the electrically charged components of stealth dark matter particles could have interacted with ordinary matter.

However, once the universe cooled, a new, powerful and as yet unknown force might have bound these component particles together tightly to form electrically neutral composites.

Stealth dark matter particles should be stable — not decaying over eons, if at all, much like protons.

However, the researchers suggest the components making up stealth dark matter particles can form different unstable composites that decay shortly after their creation.

These unstable particles might have masses of about 100 billion electron-volts or more, and could be created by particle accelerators such as the Large Hadron Collider (LHC) beneath the France-Switzerland border. They could also have an electric charge and be visible to particle detectors, Vranas said.

Experiments at the LHC, or sensors designed to spot rare instances of dark matter colliding with ordinary matter, “may soon find evidence of, or rule out, this new stealth dark matter theory,” Vranas said in a statement.

If stealth dark matter exists, future research can investigate whether there are any effects it might have on the cosmos.

The scientists, the Lattice Strong Dynamics Collaboration, will detail their findings in an upcoming issue of the journal Physical Review Letters.

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Pass it on: New Scientist