Milky Way-like

Milky Way-like galaxy found in deep space puzzles astronomers – CNET


SPT0418-47 is gravitationally-lensed by another galaxy, giving it an evil Eye of Sauron look to our telescopes.

ALMA (ESO/NAOJ/NRAO)/Rizzo et al.

Twelve billion years ago, when all of space was just a fledgling baby universe, a young galaxy reminiscent of the Milky Way was flaring to life deep in the cosmos. Astronomers have often thought of this early universe as a chaotic, extreme environment where galaxies are unstable and violent. New research suggests those assumptions may be incorrect, providing new insight into how galaxies form.

In a new study, published in the journal Nature on Wednesday, observations made by Chile’s Atacama Large Millimeter/submillimeter Array (ALMA) of SPT–S J041839–4751.9, or SPT0418-47 for short, show the infant galaxy has features similar to those of our own more mature Milky Way. Light from the galaxy took 12 billion years to reach us. That means astronomers are looking back in time at a galaxy that formed less than 1.5 billion years after the birth of the universe.  

Previous modeling and observations have led astronomers to theorize that the period after the universe’s birth was tumultuous. Early galaxies were likely smashing into each other and merging to form big, disordered masses of stars. They shouldn’t settle down into neat, flat disks. But SPT0418-47 does, and that’s quite a surprise that upends some of our beliefs about early cosmic activities in the universe.

“This result represents a breakthrough in the field of galaxy formation, showing that the structures that we observe in nearby spiral galaxies and in our Milky Way were already in place 12 billion years ago,” Francesca Rizzo, an astronomy Ph.D. student at Germany’s Max Planck Institute for Astrophysics and first author on the study, said in a statement.   

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Because SPT0418-47 is so far away, it’s difficult to locate in the sky because its light is so faint. To find and characterize SPT0418-47, the research team took advantage of a phenomenon known as “gravitational lensing.” Light from distant galaxies does not travel on a straight line to Earth — it’s influenced by the effects of gravity on its way here. Nearby galaxies distort and reshape the light from more distant galaxies as it travels to our telescopes.

But lensing can aid detection. Using the technique and the ALMA telescope, researchers were able to magnify the light from SPT0418-47 and boost the resolution to observe the young galaxy’s features. The effect of the lensing means images obtained by ALMA shows SPT0418-47 as an aggressive, fiery Eye of Sauron-type ring, a perfect circle of light containing hundreds of thousands of stars.

Using computer modeling techniques, the research team took the gravitationally lensed, circular images of SPT0418-47 and reconstructed what the galaxy would look like if our telescopes were powerful enough to see that far on their own (as the video below demonstrates). The modeling reshaped the galaxy in a surprising way.

“When I first saw the reconstructed image of SPT0418-47 I could not believe it,” Rizzo said. “A treasure chest was opening.” 

The reconstruction showed SPT0418-47 doesn’t quite have the large, spiral arms we’re used to seeing in the Milky Way, but it does have a disc and a giant bulge at its center, reminiscent of our home galaxy. The European Southern Observatory suggest it’s a Milky Way lookalike. 

“It’s less of a lookalike and more of a mini-me,” says Sarah Martell, an astrophysicist at the University of New South Wales who was not affiliated with the study. “It’s only 25% of the mass of the Milky Way and half the size.”

But what it lacks in stature it makes up for in star power. The galaxy’s star formation rate is equivalent to the mass of 350 of our own suns, which Martell calls “enormous.” By comparison, she notes, the Milky Way’s star formation rate is just 1.6 solar masses per year. Simona Vegetti notes the star formation rate is “quite puzzling,” because it signifies the galaxy as a site of highly energetic processes. Presumably, this would lead to more disorder, but SPT0418-47 remains cool and calm even with all of that activity.

The young galaxy won’t evolve into a Milky Way-type spiral galaxy like those we’re familiar with today. Instead, the researchers believe it will become an elliptical galaxy like Messier 87, where the first images of a black hole were captured. Such a fate won’t occur for millions of years. However, when the European Southern Observatory’s Extremely Large Telescope comes online in 2025, it’s likely astronomers will find more of these ordered galaxies, allowing them to uncover how they might form and evolve in the early universe.

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Hurtling Milky

Star Hurtling around Milky Way’s Central Black Hole Validates Einstein’s General Relativity | Astronomy –

At the center of the Milky Way lurks Sagittarius A*, a supermassive black hole that is four million times the mass of the Sun. Located 26,000 light-years away, Sagittarius A* and a dense star cluster around it provide a unique laboratory for testing physics in an otherwise unexplored and extreme regime of gravity. One of these stars, S2 (also known as S0-2), sweeps in towards Sagittarius A* to a closest distance less than 20 billion km. At its closest approach to the black hole, S2 is hurtling through space at almost 3% of the speed of light, completing an orbit once every 16 years. New observations made with ESO’s Very Large Telescope (VLT) have revealed that S2 moves just as predicted by Einstein’s general theory of relativity. Its orbit is shaped like a rosette and not like an ellipse as predicted by Newton’s theory of gravity.

This simulation shows the orbits of stars very close to Sagittarius A*, a supermassive black hole at the heart of the Milky Way. One of these stars, S2, orbits every 16 years and is passing very close to the black hole in May 2src18. Image credit: ESO / L. Calçada /

This simulation shows the orbits of stars very close to Sagittarius A*, a supermassive black hole at the heart of the Milky Way. One of these stars, S2, orbits every 16 years and is passing very close to the black hole in May 2018. Image credit: ESO / L. Calçada /

Most stars and planets have a non-circular orbit and therefore move closer to and further away from the object they are rotating around.

S2’s orbit precesses, meaning that the location of its closest point to the supermassive black hole changes with each turn, such that the next orbit is rotated with regard to the previous one, creating a rosette shape.

General relativity provides a precise prediction of how much its orbit changes and the latest measurements from this research exactly match the theory.

This effect, known as Schwarzschild precession, had never before been measured for a star around a supermassive black hole.

“After following the star in its orbit for over two and a half decades, our exquisite measurements robustly detect S2’s Schwarzschild precession in its path around Sagittarius A*,” said Dr. Stefan Gillessen, an astronomer in the Max Planck Institute for Extraterrestrial Physics.

“Einstein’s general relativity predicts that bound orbits of one object around another are not closed, as in Newtonian gravity, but precess forwards in the plane of motion,” said Dr. Reinhard Genzel, Director of the Max Planck Institute for Extraterrestrial Physics and a researcher at the University of California, Berkeley.

“This famous effect — first seen in the orbit of the planet Mercury around the Sun — was the first evidence in favor of general relativity.”

“One hundred years later we have now detected the same effect in the motion of a star orbiting the compact radio source Sagittarius A* at the center of the Milky Way.”

“This observational breakthrough strengthens the evidence that Sagittarius A* must be a supermassive black hole of 4 million times the mass of the Sun.”

The study also helped the astronomers learn more about the vicinity of Sagittarius A*.

“Because the S2 measurements follow general relativity so well, we can set stringent limits on how much invisible material, such as distributed dark matter or possible smaller black holes, is present around Sagittarius A*,” said Observatoire de Paris astronomer Dr. Guy Perrin and Dr. Karine Perraut from the Universite Grenoble Alpes.

“This is of great interest for understanding the formation and evolution of supermassive black holes.”

The findings appear in the journal Astronomy & Astrophysics.


R. Abuter et al (GRAVITY Collaboration). 2020. Detection of the Schwarzschild precession in the orbit of the star S2 near the Galactic centre massive black hole. A&A 636, L5; doi: 10.1051/0004-6361/202037813

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