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Ghostly galaxy without dark matter stuns astronomers

To find an explanation, the team is already hunting for more dark-matter deficient galaxies as they analyse Hubble images of 23 ultra-diffuse galaxies

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Countless galaxies exist in the universe, each hiding secrets that humankind is yet to unearth. Pixabay
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  • Astronomers discovered galaxy missing its dark matter
  • Dark matter is believed to be integral to any galaxy
  • It is the glue which holds everything together

In a shocking discovery, astronomers have found a galaxy that is missing most — if not all — of its dark matter. This discovery of the galaxy NGC 1052-DF2, detailed in the journal Nature, challenges currently-accepted theories of and galaxy formation and provides new insights into the nature of dark matter.

Black hole in milky way
Astronomers discovered a galaxy missing its dark matter. VOA

“Dark matter is conventionally believed to be an integral part of all galaxies — the glue that holds them together and the underlying scaffolding upon which they are built,” explained study co-author Allison Merritt from Yale University in the US and the Max Planck Institute for Astronomy, Germany.

“This invisible, mysterious substance is by far the most dominant aspect of any galaxy. Finding a galaxy without any is completely unexpected; it challenges standard ideas of how galaxies work,” said lead researcher Pieter van Dokkum of Yale University. “There is no theory that predicts these types of galaxies — how you actually go about forming one of these things is completely unknown,” Merritt said.

For the study, the researchers used the NASA/European Space Agency’s Hubble Space Telescope and several other observatories. Hubble helped to accurately confirm the distance of NGC 1052-DF2 to be 65 million light-years and determined its size and brightness.

Saraswati
Dark matter is the glue which holds everything together in a galaxy. Wikimedia

Based on these data the team discovered that the newly discovered galaxy is larger than the Milky Way, but contains about 250 times fewer stars, leading it to be classified as an ultra diffuse galaxy. “I spent an hour just staring at this image,” van Dokkum said as he recalled first seeing the Hubble image of NGC 1052-DF2.

“This thing is astonishing: a gigantic blob so sparse that you see the galaxies behind it. It is literally a see-through galaxy,” he added. Further measurements of the dynamical properties of 10 globular clusters orbiting the galaxy allowed the team to infer an independent value of the galaxies mass.

This mass is comparable to the mass of the stars in the galaxy, leading to the conclusion that NGC 1052-DF2 contains at least 400 times less dark matter than astronomers predict for a galaxy of its mass, and possibly none at all.

Also Read: Milky Way’s neighbouring galaxy is of same size, not bigger

This discovery is unpredicted by current theories on the distribution of dark matter and its influence on galaxy formation. The discovery of NGC 1052-DF2 demonstrates that dark matter is somehow separable from galaxies. This is only expected if dark matter is bound to ordinary matter through nothing but gravity.

Cosmic rays
Dark matter is integral to all galaxies. Pixabay

Meanwhile, the researchers already have some ideas about how to explain the missing dark matter in NGC 1052-DF2. Did a cataclysmic event such as the birth of a multitude of massive stars sweep out all the gas and dark matter? Or did the growth of the nearby massive elliptical galaxy NGC 1052 billions of years ago play a role in NGC 1052-DF2’s dark matter deficiency?

These ideas, however, still do not explain how this galaxy formed. To find an explanation, the team is already hunting for more dark-matter deficient galaxies as they analyse Hubble images of 23 ultra-diffuse galaxies — three of which appear to be similar to NGC 1052-DF2. IANS

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A Dozen New Moons Found Orbiting Jupiter

Twelve new moons orbiting Jupiter have been found -- 11 'normal' outer moons, and one that they're calling an 'oddball.'

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Jupiter
Astronomers Discovers 12 New Moons Orbiting Around Jupiter. (VOA)

Astronomers are still finding moons at Jupiter, 400 years after Galileo used his spyglass to spot the first ones.

The latest discovery of a dozen small moons brings the total to 79, the most of any planet in our solar system.

Scientists were looking for objects on the fringes of the solar system last year when they pointed their telescopes close to Jupiter’s backyard, according to Scott Sheppard of the Carnegie Institute for Science in Washington. They saw a new group of objects moving around the giant gas planet but didn’t know whether they were moons or asteroids passing near the planet.

“There was no eureka moment,” said Sheppard, who led the team of astronomers. “It took a year to figure out what these objects were.”

They all turned out to be moons of Jupiter. The confirmation of 10 was announced Tuesday. Two were confirmed earlier.

The moons had not been spotted before because they are tiny. They are about one to two kilometers across, said astronomer Gareth Williams of the International Astronomical Union’s Minor Planet Center.

And he thinks Jupiter might have even more moons just as small waiting to be found.

“We just haven’t observed them enough,” said Williams, who helped confirm the moons’ orbits.

Jupiter
12 New Moons Discovered Orbiting Jupiter. Pixabay

The team is calling one of the new moons an “oddball” because of its unusual orbit. Sheppard’s girlfriend came up with a name for it: Valetudo, the great-granddaughter of the Roman god Jupiter.

Valetudo is in Jupiter’s distant, outer swarm of moons that circles in the opposite direction of the planet’s rotation. Yet it’s orbiting in the same direction as the planet, against the swarm’s traffic.

“This moon is going down the highway the wrong way,” Sheppard said.

Scientists believe moons like Valetudo and its siblings appeared soon after Jupiter formed. The planet must have acted like a vacuum, sucking up all the material that was around it. Some of that debris was captured as moons.

“What astonishes me about these moons is that they’re the remnants of what the planet formed from,” he said.

Telescopes in Chile, Hawaii and Arizona were used for the latest discovery and confirmation.

Also Read-NASA Probes Unveils Stormy Environment of Jupiter’s moon

Galileo detected Jupiter’s four largest moons, Io, Europa, Ganymede and Callisto, in 1610. The latest count of 79 known moons includes eight that have not been seen for several years. Saturn is next with 61, followed by Uranus with 27 and Neptune with 14. Mars has two, Earth has one and Mercury and Venus have none. (VOA)