Timeline of the Discovery
Provided by the Space Telescope Science Institute:
1987
A British team finds pulsar, PSR B1620-26, in the core of M4, a globular cluster about 7,000 light-years away. It is suspected to be part of a binary system, with the companion a white dwarf star. But the team has to wait half the white dwarf’s orbit time (200 days) to confirm it.
1988
The team publishes the discovery paper. Since it is one of the first of its kind to be discovered, the pulsar sparks many follow-up papers describing how the neutron star became a pulsar and explaining the white dwarf’s origins.
1990-92
Using pulsar timing, three groups find an anomaly in the pulsar’s signal indicating it is being gravitationally pulled by one or more unseen objects.
1992
At a conference, Don Backer of UC Berkeley presents a paper contending that the anomaly discovered using pulsar timing is a third object in the system. At the same conference, Steinn Sigurdsson proposes that "it might be possible to see planets "stolen" from their parent stars by pulsars."
1993
In just one year, four papers are published discussing possible explanations
for the anomaly in the system. Theories for the object’s celestial designation
range from a black hole to a Saturn-like planet. Debates run high as this list
of third-body candidates grows.
At this time Sigurdsson presents his paper on the anomaly in which he rejects
several different models to predict the exchange interaction scenario. Shortly
afterward, scientists rule out the possibility of a black hole. This implies
that it is a half solar mass star or a Jupiter-sized planet.
Even more papers are now published, most concerning the orbits of the system’s
objects. Within the current scope of knowledge about the system, the white dwarf’s
orbit should be perfectly circular, but turns out to be slightly elliptical,
like Earth’s orbit, which is a great surprise. In addition, the eccentricity
of the third object, predicted to be quite large, is instead rather small. Because
of such ongoing uncertainties, many new explanations for the system arise, including
reformed theories about the evolution of the system after it settled into its
current configuration.
1995-96
Multiple parties begin to look for a proposed third star in the system. One team claims to have found it, but it is discovered instead to be a nearby star that is not actually in the system. Following that close call, new theories about the possibilities of a faint cold star or a white dwarf arise.
1999
After more than 10 years of perplexity over this system, a paper is published
analyzing a decade’s worth of data concerning this system. The system is subsequently
observed in radio wavelengths, but scientists still possess no complete answer
because there is no data about the system’s tilt. An unknown inclination gives
researchers a wide range of possibilities.
Later, however, individual probabilities are calculated for different solutions.
Researchers find there to be a low chance that the third body is a star; rather,
they find a higher probability of the object being a low-mass object, like a
Jupiter-mass planet or brown dwarf.
2000
A student’s theory paper suggests a mechanism for the planet being in the system. This is a well-known effect to explain the squished orbit of the white dwarf, but researchers had yet to apply it to this situation.
2000-present
Hubble data sets, one taken starting in 1995 and another recent one, are compared
to distinguish the movement of the white dwarf within the cluster. After a long
wait, scientists are now able to determine the white dwarf’s true mass, inclination,
time of formation, and the age of the system.
This new data boosts enormously the probability of the object being a planet.
Determination of the planet’s inclination is now possible, because all three
components are not coplanar.
From this calculation, the team is able to find the mass of the planet.
advertisement
