Astronomy - USA (2022-06)

8 ASTRONOMY • JUNE 2022

JUST OVER 4 LIGHT-YEARS AWAY IS PROXIMA CENTAURI, the closest star

to the Sun. In August 2016, researchers found a planet circling this star. Then,

in January 2020, they spotted a second world. And now, Proxima’s family tree is

growing again: A third terrestrial planet has been found.

In a study published Feb. 10 in Astronomy & Astrophysics, astronomers

announced the discovery of Proxima d. This tiny planet is just one-quarter the

mass of Earth and orbits Proxima Centauri every five days at less than one-tenth

Mercury’s distance from our Sun. Because Proxima Centauri is a red dwarf, this

puts Proxima d in the star’s habitable zone, where conditions are right for liquid

water to exist on its surface.

Third planet found

around Proxima Centauri

THIRD ROCK. An artist’s impression shows the small

world Proxima d orbiting the Sun’s nearest neighbor,

Proxima Centauri. ESO/L. CALÇADA

QUANTUM GRAVITY

All large galaxies host supermas-

sive black holes weighing millions

or billions of times the Sun’s mass.

Some are actively sucking in material,

releasing energy in the process. These

are called active galactic nuclei, or AGN,

and astronomers have recently taken a

close look at the one within the galaxy

M77, some 47 million light-years away.

Detailed imagery shows the AGN is

completely cloaked within a ring of gas

and dust. The view is not just spectacu-

lar, but it also confirms a long-standing

theory that explains why we see many

types of AGN. The work was published

Feb. 16 in Nature.

POINT OF VIEW

AGN range from bright beacons scream-

ing at us across the electromagnetic

spectrum (type 1) to those that glow

softly only in low-energy light, such

as infrared (type 2).

The leading explanation for this

variety is the unified model. This

theory holds that although we see

different types of AGN across the

universe, there aren’t a variety of black

holes. Ultimately, all AGN are inher-

ently the same, comprising a feeding

BLACK HOLE’S CLOSE-UP

CONFIRMS THEORY

M77’s central black hole sports a ring of dust — as expected.

ZOOMED IN. At the center of galaxy

M77 (which is shown at upper left in

optical light) is a dusty disk hiding

a supermassive black hole, whose

light is reprocessed into infrared

wavelengths and pictured at right.

ESO/JAFFE, GÁMEZ-ROSAS ET AL.