Astronomy

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temperature and pressure.
Objects above that threshold
are stars. Brown dwarfs ini-
tially produce heat by fusing an
isotope of hydrogen called deu-
terium into helium-3, which
can occur at lower tempera-
tures and thus, lower masses.
TRAPPIST-1, an ultra-cool
dwarf star, is 84 Jupiter masses.
The largest known brown
dwarf is 90 Jupiter masses. In
other words, the realm of large
brown dwarfs and small stars is
a bit murky.
Astronomers discovered the
first brown dwarf in 1995, the
same year they confirmed the
first planet around a Sun-like
star. So, what happened to vB8’s
companion 11 years earlier?
The vB8 discovery sent
shock waves through the astro-
nomical community; a confer-
ence was convened in 1986 on
the topic of brown dwarfs.
According to New Light on
Dark Stars by I. Neill Reid and
Suzanne L. Hawley, that very
conference torpedoed the case
for vB8’s companion, as other
infrared observations failed to
find it. “The only possible con-
clusion is that the original
detection was an observational
artefact, probably due to the
chromatic effects of atmo-
spheric refraction,” they write.
The first planet — or pos-
sibly the first brown dwarf —
evaporated almost as quickly as
it had emerged.

Pulsar planets
In 1992, astronomers officially
found the first planetary sys-
tem when they discovered two
(later found to be three) objects
around PSR B1257+12, a pulsar
2,300 light-years away. Pulsars

— a type of rapidly rotating

neutron star — are often too

small to be seen in optical light,

so the planets’ presence was

inferred from subtle changes in

the normally precise radio sig-

nals coming from the pulsar.

Pulsar planets are weird

— neutron stars are formed in

supernovae or stellar mergers,

violent events that tend to con-

sume or sweep away materials

from any planet in the vicinity,

destroying them. Thus, the

scant few pulsar planets discov-

ered to date are likely to have

formed after the supernova in a

second planetary genesis.

A year earlier, in 1991, there

were claims of a planet around

PSR B1829−10, a different pul-

sar 30,000 light-years away.

The progression of papers in

the journal Nature tells it all. In

August 1991, a trio of astrono-

mers published their results: “A

planet orbiting the neutron star

PSR 1829–10.” But a January

1992 paper by two of the three

original authors was titled “No

planet orbiting PSR 1829–10.”

The planet detection had been

a simple miscalculation created

by failing to model Earth’s

orbit accurately when assessing

measurements of the star.

The 1991 claim wasn’t even

the first possible pulsar planet

that never was. In a November

1979 Nature letter, Mieczysław

Prószyński and Marek

Demiański of Warsaw

University found timing varia-

tions in pulsar PSR 0329+54

suggesting something was

affecting the dense star husk.

They proposed a change in

shape, a change in magnetic

fields, or a planet half the mass

of Earth (or less) orbiting it. A

1995 article by Tatiana V.

Shabanova in The Astrophysical

Journal tried to bolster the case,

but subsequent investigations

found the signal variations are

likely a consequence of the

star’s variable rotation rate.

There is also an October 22,

1969, article in The New York

Times asserting a planet orbit-

ing the Crab pulsar, based on a

“wobble” observed in the pulsar

that could be like the wobble

that occurs in the Sun as the

planets orbit. The results were

published in Nature in 1970,

but subsequent papers on the

wobble observed in the Crab

and Vela pulsars suggested that

it was instead caused by stresses

and friction in the star’s crust,

leading to starquakes.

Gamma Cephei

Some planet stories have a

happy ending.

Gamma (γ) Cephei A was

initially thought to have a

planetary-mass companion in

1988, though the evidence was

only tentative. At the time, the

emerging technology of radial

velocity was just barely refined

enough to detect planets.

The 1988 data did confirm

one thing: Gamma Cephei was

a binary star system with a low-

mass red dwarf, Gamma

Cephei B, circling Gamma

Cephei A. Even after account-

ing for the companion’s effects,

Stephenson Yang and his asso-

ciates still saw evidence in their

signal for a low-mass, possibly

planetary object in the system.

But a 1992 follow-up study

cast doubt on the tentative

planet. Gamma Cephei B dom-

inated the radial velocity mea-

surements, making the

supposed planet’s signal scien-

tifically unreliable. “We had a

very weak signal, one and a half

sigma,” says Yang, a professor

at the University of Victoria

and a principal investigator.

Also, Gamma Cephei A was

believed to be much younger

than it actually is. “We thought

we were looking at a much

more variable star than one that

was main sequence,” Yang says.

They chalked up their weak

signal to variations in the star

and retracted their planetary

claim.

Fast-forward to 2003. A

planet around Gamma Cephei

A was announced with roughly

the mass and orbit suggested by

the 1988 results. Yang and his

compatriots had, in fact, found

the first exoplanet. They just

hadn’t been able to confirm it.

In 1992, Gamma Cephei B

wasn’t well constrained. By

gathering more data, it was

possible to extract the signature

of the smaller star from the

wobbles of Gamma Cephei A.

And from that information, a

Jupiter-sized world with a

2.5-Earth-year orbit emerged.

“When you look at the radial

velocity of the star, you do see a

large radial velocity change

because it has a companion,”

Yang says. “If you took out the

changes, you see ripples, which

[are] caused by the planet.”

And thus, a planet called

Gamma Cephei Ab was found

around a future North Star,

based on the small changes it

makes to its star’s orbit, which

had been drowned out by the

tug of a much larger star.

“I still remember the first

time we looked at the ripple

and said, ‘Oh wow, it fits so

nicely to the orbit,’ ” Yang says.

So 51 Pegasi b got the glory.

But Gamma Cephei Ab was

there first. (Fischer also points

out HD 114762b, which was

discovered in 1989 and con-

firmed in 2012. Technically it

could be considered the second,

bumping 51 Pegasi b to third.)

A nearly 150-year hunt had

drawn to a close. Now armed

with a few confirmed planets,

astronomers could begin to

build a real catalog of stars with

planetary systems. All it took

was a handful of phantom

planets to get there.

John Wenz is an associate editor

of Astronomy magazine.

Stephenson Yang