Astronomy

ASTRONEWS

18 ASTRONOMY • SEPTEMBER 2017

Weirdest star gets weird again

Astronomers recently discovered that

dwarf planet 2007 OR 10 , the largest

known body in the solar system with

no common name, has a moon. 2007

OR 10 was discovered in 2007 by Meg

Schwamb, a graduate student who

was working with planetary scientist

Mike Brown at the time. With a diameter

between 800 and 950 miles (1,290–

1,528km), it’s the third- or fourth-largest

object known in the Kuiper Belt after

Pluto, Eris, and Makemake.

There is some debate about its size.

Brown lists it as the fourth-largest,

while other estimates place it above

Makemake in diameter. It is a red, icy

world that swings from 33 to 101

astronomical units in its orbit. (An AU is

the distance between Earth and the

Sun; Neptune is at 30 AU.)

OR 10 has a slow rotation rate, which

hid the moon in plain sight from

Hubble for quite some time. The moon

is large for OR 10 ’s size, estimated

at 150–250 miles (240–400km) in

diameter. The higher estimate would

place the moon at the lower limit of

dwarf planet status, if it orbited the Sun

on its own. A body is considered a

dwarf planet if it can attain a round

shape and is only in orbit around the

Sun and not another body. The moon

is about one-quarter the size of OR 10 ,

a ratio similar to the Earth-Moon

system.

Maybe this large moon will boost the

case for giving the dwarf planet a real

name. — J. W.

Nameless rock has another rock around it A star 1,300 light-years away exhibits some of the strangest

behavior ever seen: Something dims its light by 20 percent,

and that something is much bigger than a planet. It’s called

KIC 8462852, but most people shorten it to Tabby’s Star or

Boyajian’s Star, for its discoverer, Tabetha Boyajian. In May,

it started dimming again, leading to a feverish search for

the cause.

No one knows what causes the dimming. It could be a

massive fleet of comets or the spread-out debris of a

planet. Boyajian and co-investigator Jason Wright put out

the alert, hoping that at least one telescope could grab a

spectrum from the star to see what is causing the dimming.

One strange hypothesis — a sort of “all other avenues

have been exhausted” — is a giant Dyson Swarm of

machines built by an alien megacivilization meant to har-

ness the star’s power. Gathering spectra could help rule out

or bolster the case for that scenario.

Professional and amateur astronomers participated in a

worldwide campaign to observe Tabby’s Star. Now we just

have to wait for the results. — J. W.

HOT DOUGHNUT. When planets or planetesimals collide, they may create an object called a synestia,

a doughnut-shaped mass of molten material that eventually reforms into a solid mass.

I SEE YOU. Hubble images between 2009 and 2010 drew out a previously unseen moon

around 2007 OR 10. NASA/STScI

WHAT’S THAT? The bizarre dimming of Tabby’s Star (KIC

8462852) has excited and confused both the astronomy community

and the public since it was discovered in Kepler data in 2015. IPAC/NASA

November 6, 2009 September 18, 2010

A new look at

the Crab Nebula

NASA, ESA, NRAO/AUI/NSF AND G. DUBNER (UNIVERSITY OF BUENOS AIRES)

A COLORFUL SIGHT. Scientists combined

data from five telescopes to produce a new,

stunning image of the Crab Nebula: the Karl

G. Jansky Very Large Array (radio) in red, the

Spitzer Space Telescope (infrared) in yellow,

the Hubble Space Telescope (visible) in green,

the XMM-Newton Observatory (ultraviolet)

in blue, and the Chandra X-ray Observatory

(X-ray) in purple. The data from the telescopes

span the entire electromagnetic spectrum to

provide an incredibly detailed picture. About

6,500 light-years from Earth, the Crab Nebula

is a magnitude 8.4 supernova remnant in the

constellation Taurus. A superdense neutron

star lives in its center, emitting radio pulses as

it rotates every 33 milliseconds. A team of sci-

entists led by Gloria Dubner of the Institute of

Astronomy and Physics, the National Council

of Scientific Research, and the University of

Buenos Aires studied the newly found details

in the image to better understand the physics

of the nebula and are reporting their results

to The Astrophysical Journal. “Comparing

these new images, made at different wave-

lengths, is providing us with a wealth of new

detail about the Crab Nebula,” Dubner said.

“Though the Crab has been studied exten-

sively for years, we still have much to learn

about it.” — N. K.