Astronomy

ASTRONEWS

12 ASTRONOMY • APRIL 2018

FREE FALLING. A French satellite experiment confirmed that the equivalence principle — a key tenet of Albert Einstein’s

general theory of relativity that states all objects fall at the same rate, despite any differences in mass — holds true in space.

As the catalog of known exoplanets grows,

astronomers continue to ask: Could any of

these planets host life? While many habit-

ability studies focus on planets capable of

hosting liquid water, some researchers are

now arguing that “water worlds” may not be

the best place to find extraterrestrial life.

During a five-day workshop in Laramie,

Wyoming, on habitable worlds last

November, some of the world’s foremost

planet hunters met to evaluate which exo-

planets are the best candidates for life. They

concluded that water alone is not the decid-

ing factor in whether life will arise, and

should not be the sole target in the search

for habitable worlds.

That’s because many other factors come

into play when creating an environment

suitable for Earth-like life. The presence of

geological activity and of vital nutrients,

such as phosphorus, are also necessary for

life to thrive on Earth. An exoplanet

sheathed in oceans with no phosphorus-

rich dry land and no geothermal activity to

heat the water and dredge up additional

nutrients is not a good place to look for life.

Furthermore, the type of star a world cir-

cles and the distance between the star and

the world can affect the chemical makeup

of the planet’s atmosphere, helping or hin-

dering the case for habitability. Winds and

storms from a planet’s host star can erode

the atmosphere if the star is too active or if

the planet’s magnetic field is too weak.

While exoplanets rich in water are likely

common, it is planets with the right mix of

water and land, geothermal activity, and

atmospheric chemistry that astronomers now

believe should be the targets in the search for

life. Narrowing down these targets will pre-

vent wasted resources when instruments like

the James Webb Space Telescope come

online, boosting the chances of finding real

signs of life in the coming decades. — A.K.

Rethinking water’s

role in search for life

In the early universe, black holes 100,000 or

more times the mass of the Sun formed fast

and often. But how they formed, especially

so quickly, remains a question. The recent

discovery of a behemoth black hole just

690 million years after the Big Bang may

help astronomers answer it.

J1342+0928 is a quasar — a big, bright

disk of infalling material — around a black

hole already containing 800 million solar

masses that formed when the universe was

just 5 percent its current age. At 13.1 billion

light-years away, it is the new record-holder

for the most distant supermassive black hole.

The quasar was found in data from three

large surveys: the DECam Legacy Survey,

NASA’s Wide-field Infrared Survey

Explorer, and the United Kingdom Infrared

Telescope Deep Sky Survey (UKIDSS) Large

Area Survey. The discovery was published

December 6 in Nature, and details about its

host galaxy appeared in The Astrophysical

Journal Letters.

The number and size of quasars in the

early universe depend on its conditions.

Current models of supermassive black hole

growth predict somewhere between 20 and

100 bright quasars as distant as J1342+

in the entire sky. And J1342+0928 is just the

second (and farthest) quasar in this group

ever found, now doubling the objects avail-

able to study at a unique time in the uni-

verse’s history: the epoch of reionization.

Immediately after the Big Bang, the uni-

verse was smaller, hotter, and denser. As it

expanded, it cooled; after 400,000 years,

it had cooled enough for particles to com-

bine and form neutral hydrogen atoms.

But nothing else was created until gravity

finally caused denser regions of hydrogen

to collapse and coalesce into stars and,

later, galaxies.

These stars and galaxies began shining,

putting out light — photons. Their photons

were capable of knocking electrons off the

neutral hydrogen gas permeating the uni-

verse, ionizing it into the state in which it

exists today. This is called the epoch of reion-

ization, and “it was the universe’s last major

transition and one of the current frontiers of

astrophysics,” said Carnegie astronomer

Eduardo Bañados, leader of the team that

discovered J1342+0928, in a press release.

Astronomers know that J1342+0928 is

shining during this time period in cosmic

history because the majority of the material

surrounding its host galaxy is neutral; it

hasn’t been ionized yet, suggesting that

J1342+0928 is one of the many ionizing

sources at work changing the universe

during this time. That makes this quasar

extremely valuable, and literally a light in

the dark, guiding astronomers to a better

understanding of what the universe was like

less than 700 million years after its birth.

— Alison Klesman

FARTHEST SUPERMASSIVE BLACK HOLE

LIES 13 BILLION LIGHT-YEARS AWAY

10.

kilometers

JUST RIGHT? Ross 128b is a recently discovered

exoplanet with a good chance of harboring liquid

water. But is water enough to sustain Earth-like life

on its surface? M. KORNMESSER/ESO

BABY PICTURE. J1342+0928 is a quasar: a supermassive black hole with a disk of material shining when

the universe was 690 million years old. Its light played a role in transforming the universe into the state in which

it remains today. ROBIN DIENEL, COURTESY OF THE CARNEGIE INSTITUTION FOR SCIENCE

The minimum possible radius of a nonrotating

neutron star with a mass of 1.6 solar masses,

according to gravitational wave measurements.