Sky & Telescope - June 2022 - 9

QUASAR LIGHT CURVE: TONY READHEAD / CALTECH; EARLY
SOLAR SYSTEM: GREGG DINDERMAN / S&T, SOURCE: J.
ALÉON / NATURE ASTRONOMY 2022
Radio flux (Jansky)
QUASARS
The variations suggest that the two
Two Black Hole Behemoths Will Merge in 10,000 Years
TWO SUPERMASSIVE black holes in
the heart of a distant galaxy are tightly
entwined, offering unique insights into
how such mergers unfold.
One of the black holes gorges on
surrounding material, creating a radio
jet that happens to point almost directly
at Earth. Such objects, called blazars,
are known for their volatility, typically
flaring and dimming randomly. But
when team member Anthony Readhead
(Caltech) began observing the blazar,
PKS 2131-021, in 2008, he noticed
something unusual. " It was varying
not just periodically, but sinusoidally, "
Readhead says.
To confirm that the years-long pattern
was real, he and his team went
4.0
3.0
2.0
1.0
0.0
1980
1990
Year
pThree sets of radio observations of the quasar PKS 2131-021, spanning 45 years, show the sinusoidal pattern in its brightness.
2000
2010
2020
MIT: Haystack Observatory
University of Michigan: Radio Astronomical Observatory
Caltech: Owens Valley Radio Observatory
trawling through older data, ultimately
going back to archived data 45 years old.
Upon seeing the peaks and troughs in
the earlier data, " we knew something
very special was going on, " says Sandra
O'Neill (also at Caltech), first author of
the paper in the February 20th Astrophysical
Journal Letters.
Theorist Roger Blandford (Stanford
University), who took on the challenge
of modeling the system, found that the
simplest explanation called for a second
black hole: The jet's brightness cycles
with the pair's orbital period.
" Before Roger worked it out, nobody
had figured out that a binary with a
relativistic jet . . . looked like this, "
explains Readhead.
supermassive black holes orbit each
other every two years about 2,000
astronomical units apart, or some 50
times the average distance between
Pluto and the Sun. The strongest closebinary
candidate previously known to
astronomers, OJ 287, takes nine years to
complete an orbit.
The black holes will keep spiraling
inward, ultimately colliding in around
10,000 years' time - an astronomical
heartbeat away. When they do, they will
unleash vast amounts of energy in the
form of gravitational waves.
The discovery excites Davide Gerosa
(University of Milano-Bicocca, Italy),
who was not involved in the research.
" It's been a long time since we've had
such a strong [binary] candidate. "
¢COLIN STUART
pristine hydrogen gas. Other minerals
containing oxidized iron had higher
D/H ratios, indicating they had encountered
traces of water vapor with a
chemical composition similar to Earth's
oceans. In other words, our planet's
water was already there in the disk as
Earth was forming.
The researchers suggest that this
water came from outside the solar
system, dragged in as the solar nebula
collapsed. Chemical reactions that had
occurred long ago in the cold space
between the stars had already enriched
its deuterium content. The fact that
This diagram shows a rough picture of the
early solar system. As the solar nebula collapsed,
a protoplanetary disk formed. An influx
of water-rich (and deuterium-rich) gas from the
interstellar medium fed the inner disk.
some of the meteorite's minerals don't
have much deuterium and the others
do suggests that the influx happened
within the first 200,000 years of the
solar system.
" This is a coherent hypothesis, " says
planetary geologist Jesús Martínez-Frías
(Complutense University of Madrid),
" and very plausible. "
¢JAVIER BARBUZANO
Outflow
Collapsing
solar nebula
H2O enriched
H or H2
Protosun
CAIs present
H2 + H2O
Expanding
protoplanetary
disk
D/H ratio
High
Low
1 a.u.
sk yand tele scope .o r g * JUNE 2022
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Sky & Telescope - June 2022

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