Sky & Telescope - USA (2020-01)

NEWS NOTES

12 JANUARY 2020 • SKY & TELESCOPE

BLACK HOLES

More Black Hole Mergers in LIGO Data

SOLAR SYSTEM

The Puzzling Clouds

of Venus

THE LIGO-VIRGO COLLABORATION

has so far announced 11 detections of

gravitational-wave surges based on data

collected during its fi rst two observ-

ing runs. Each surge comes from the

merger of distant compact objects. Now,

an independent team sorting through

the public data archive has found seven

additional black hole merger candidates.

Tejaswi Venumadhav (Institute for

Advanced Study) and his colleagues

developed their own data analysis pipe-

line to look specifi cally for black hole

mergers. This is unlike the approach

taken by the LIGO and Virgo collabora-

tions, who look at data with “eyes wide

open” to catch anything and every-

thing, explains LIGO spokesperson

Patrick Brady (University of Wisconsin,

Milwaukee). The more focused approach

provides greater sensitivity to spot qui-

eter signals, Venumadhav said during a

recent colloquium at Harvard Univer-

sity’s Black Hole Initiative.

The seven merger candidates

involved black holes with masses similar

to those seen crashing together by the

LIGO-Virgo Collaboration, roughly 20

to 40 solar masses. Also similar to the

LIGO-Virgo mergers, most of the new

candidates had small effective spins. The

effective spin compares the speed and

tilt of the two black holes’ individual

spins relative to each other and to their

orbit around each other. If a system has

an effective spin near zero, the most

likely reason is that the two black holes

either weren’t spinning fast before the

merger or they were spinning but were

rolling on their sides relative to their

orbit around each other.

However, one candidate, GW151216,

bucks that trend. Its high effective spin

might mean that, before the merger, the

two black holes had similar masses and

were whirling around each other like

two upright tops on a table. Or, it could

be that one fast- and upright-spinning

pA false-color image shows what Venus looks

like at infrared and ultraviolet wavelengths.

JAPAN’S AKATSUKI SPACECRAFT has

revealed previously unknown dynam-

ics in the Venusian atmosphere, say

scientists in two teams who presented

their research at the joint meeting of

the European Planetary Science Con-

gress and the American Astronomical

Society’s Division for Planetary Sciences

in Geneva, Switzerland.

The researchers’ fi ndings relate to the

superrotation of Venus’s upper atmo-

sphere, which moves faster than the

planet’s surface turns. Venus takes 243

Earth days to complete a single rotation,

but its atmosphere whisks around the

planet in just four Earth days.

Kiichi Fukuya, Takeshi Imamura

(both at the University of Tokyo), and

colleagues used Akatsuki’s Longwave

Infrared Camera to observe cloud

temperatures on the nightside as well as

the dayside. These observations revealed

black hole was more massive and thus

“outweighed” its slower partner.

The LIGO and Virgo collaborations

have been discu ssing the results with

Venumadhav’s team for about a year,

and Brady for one thinks the analysis

is sound. The collaboration plans to

release the second catalog of events

around April 2020, which will include

candidates found in the third observing

run’s fi rst six months.

■ CAMILLE M. CARLISLE

• Read about the newfound black hole
  mergers at https://is.gd/newmergers.

mottling and streaks in the cloud cover,

which the researchers tracked. While

previous ultraviolet studies of the day-

side had found that clouds tend to drift

toward the poles, the infrared observa-

tions revealed that this trend reverses at

night, when the clouds sometimes move

equatorward instead.

According to Imamura, the contrast-

ing cloud motions could be associated

with so-called thermal tides, planet-scale

atmospheric waves generated when the

Sun heats the uppermost cloud layer.

The gas heats up and moves either

toward higher altitudes or around to

the cooler nightside. This process could

accelerate equatorial cloudtops, goading

them into superrotation.

Another factor plays a role in deter-

mining wind speeds, says a group of

researchers led by Takeshi Horinouchi

(Hokkaido University, Japan) and Yeon

Joo Lee (Technical University of Berlin).

They reported that the winds tend to be

faster in the southern hemisphere than

in the northern hemisphere. This differ-

ence could be linked to the distribution

of a substance that absorbs ultraviolet

radiation. As this “unknown absorber”

affects how much heat the atmosphere

takes in, variability in its abundance

would also affect wind speeds.

■ JAVIER BARBUZANO

• The BepiColombo spacecraft will
  briefl y visit Venus in 2020. Learn what’s
  in store: https://is.gd/Venus2020.

Artist’s illustration of two black

holes about to merge

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