ALMA spots twinkling heart of Milky Way

Related Articles

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) found quasi-periodic flickers in millimeter-waves from the center of the Milky Way, Sagittarius (Sgr) A*.

The team interpreted these blinks to be due to the rotation of radio spots circling the supermassive black hole with an orbit radius smaller than that of Mercury. This is an interesting clue to investigate space-time with extreme gravity.

“It has been known that Sgr A* sometimes flares up in millimeter wavelength,” tells Yuhei Iwata, the lead author of the paper published in the Astrophysical Journal Letters and a graduate student at Keio University, Japan. “This time, using ALMA, we obtained high-quality data of radio-wave intensity variation of Sgr A* for 10 days, 70 minutes per day. Then we found two trends: quasi-periodic variations with a typical time scale of 30 minutes and hour-long slow variations.”

 

Astronomers presume that a supermassive black hole with a mass of 4 million suns is located at the center of Sgr A*. Flares of Sgr A* have been observed not only in millimeter wavelength, but also in infrared light and X-ray. However, the variations detected with ALMA are much smaller than the ones previously detected, and it is possible that these levels of small variations always occur in Sgr A*.

The black hole itself does not produce any kind of emission. The source of the emission is the scorching gaseous disk around the black hole. The gas around the black hole does not go straight to the gravitational well, but it rotates around the black hole to form an accretion disk.

The team focused on short timescale variations and found that the variation period of 30 minutes is comparable to the orbital period of the innermost edge of the accretion disk with the radius of 0.2 astronomical units (1 astronomical unit corresponds to the distance between the Earth and the Sun: 150 million kilometers). For comparison, Mercury, the solar system’s innermost planet, circles around the Sun at a distance of 0.4 astronomical units. Considering the colossal mass at the center of the black hole, its gravity effect is also extreme in the accretion disk.

“This emission could be related with some exotic phenomena occurring at the very vicinity of the supermassive black hole,” says Tomoharu Oka, a professor at Keio University.

Their scenario is as follows. Hot spots are sporadically formed in the disk and circle around the black hole, emitting strong millimeter waves. According to Einstein’s special relativity theory, the emission is largely amplified when the source is moving toward the observer with a speed comparable to that of light. The rotation speed of the inner edge of the accretion disk is quite large, so this extraordinary effect arises. The astronomers believe that this is the origin of the short-term variation of the millimeter emission from Sgr A*.

The team supposes that the variation might affect the effort to make an image of the supermassive black hole with the Event Horizon Telescope. “In general, the faster the movement is, the more difficult it is to take a photo of the object,” says Oka. “Instead, the variation of the emission itself provides compelling insight for the gas motion. We may witness the very moment of gas absorption by the black hole with a long-term monitoring campaign with ALMA.” The researchers aim to draw out independent information to understand the mystifying environment around the supermassive black hole.

NATIONAL INSTITUTES OF NATURAL SCIENCES

Header Image – Hot spots circling around the black hole could produce the quasi-periodic millimeter emission detected with ALMA. Credit : Keio University

Download the HeritageDaily mobile application on iOS and Android

More on this topic

LATEST NEWS

Prehistoric killing machine exposed

Judging by its massive, bone-crushing teeth, gigantic skull and powerful jaw, there is no doubt that the Anteosaurus, a premammalian reptile that roamed the African continent 265 to 260 million years ago - during a period known as the middle Permian - was a ferocious carnivore.

Noushabad – The Hidden Underground City

Noushabed, also called Oeei or Ouyim is an ancient subterranean city, built beneath the small town of Nushabad in present-day Iran.

10 British Iron Age Hill Forts

A hill fort is a type of earthworks used as a fortified refuge or defended settlement, located to exploit a rise in elevation for defensive advantage.

Stabiae – The Roman Resort Buried by Mount Vesuvius

Stabiae was an ancient Roman town and seaside resort near Pompeii, that was largely buried during the AD 79 eruption of Mount Vesuvius in present-day Italy.

Astronomers Accurately Measure the Temperature of Red Supergiant Stars

Red supergiants are a class of star that end their lives in supernova explosions. Their lifecycles are not fully understood, partly due to difficulties in measuring their temperatures. For the first time, astronomers develop an accurate method to determine the surface temperatures of red supergiants.

Researchers Overturn Hypothesis That Ancient Mammal Ancestors Moved Like Modern Lizards

The backbone is the Swiss Army Knife of mammal locomotion. It can function in all sorts of ways that allows living mammals to have remarkable diversity in their movements.

Archaeologists Discover one of Poland’s Largest Megalithic Tomb Complexes

Archaeologists excavating in Poland have discovered a large megalithic complex, containing several dozen tombs dating from 5500 years ago.

New Technology Allows Scientists First Glimpse of Intricate Details of Little Foot’s Life

In June 2019, an international team brought the complete skull of the 3.67-million-year-old Little Foot Australopithecus skeleton, from South Africa to the UK and achieved unprecedented imaging resolution of its bony structures and dentition in an X-ray synchrotron-based investigation at the UK's national synchrotron, Diamond Light Source.

Popular stories

Ani – The Abandoned Medieval City

Ani is a ruined medieval city, and the former capital of the Bagratid Armenian kingdom, located in the Eastern Anatolia region of the Kars province in present-day Turkey.

Interactive Map of Earth’s Asteroid and Meteor Impact Craters

Across the history of our planet, around 190 terrestrial impact craters have been identified that still survive the Earth’s geological processes, with the most recent event occurring in 1947 at the Sikhote-Alin Mountains of south-eastern Russia.

The Sunken Town of Pavlopetri

Pavlopetri, also called Paulopetri, is a submerged ancient town, located between the islet of Pavlopetri and the Pounta coast of Laconia, on the Peloponnese peninsula in southern Greece.

Exploring the Avebury Stone Circle Landscape

The area was designated part of the Stonehenge, Avebury and Associated Sites by UNESCO in 1986, in recognition for one of the most architecturally sophisticated stone circles in the world, in addition to the rich Neolithic, and Bronze age remains found nearby, such as the West Kennet Avenue, Beckhampton Avenue, West Kennet Long Barrow, the Sanctuary, and Windmill Hill.