A few months ago, on February 11, there
was an announcement from LIGO. It had detected a signal from a pair
of a black holes - the first direct detection of gravitational waves.
The signal was actually detected the previous September, but
announced in February.
However there were other events. The
process works this way: when an event occurs, computer algorithms
very quickly sort events into “probably noise from a terrestrial
event such as a truck passing nearby” and “probably a real event
from black holes or neutron stars.” If the event is a real event,
the algorithm estimates the mass of the black holes or neutron stars
involved. For some background information on how these algorithms
work see
When there are “probably real”
events, additional analysis is done on the data and this analysis
takes time. This is the reason for the delay between the event
detection and the public announcement.
Shortly after the February
announcement, there were already rumors of additional events. You'll
have to forgive me, I was aware of these rumors, but did not report
on it until now – nevertheless I had good reason to believe they
were almost certainly true. We now have official confirmation they
were true. A second event had been detected in December and was
announced last week. See this article from New York Times science
writer Dennis Overbye:
What happens now? Almost certainly
there are and/or will be additional events beyond the two we know
about, and we should see announcements of these events over time.
Also in the near future, additional facilities similar to LIGO will
come on line. These facilities will allow researchers to make more
precise determinations of the direction the gravitational waves are
coming from, possibly allowing the source of the waves to be located.
Unfortunately ground based
gravitational wave detectors are limited in the frequencies they are
able to detect. For this reason, there have been plans to place
detectors in space. The first such plan was LISA. A set of spacecraft
in space would perform measurements similar to what LIGO does, but
because they are not attached to a solid object (namely the earth),
they can respond to a wider range of frequencies, allowing a wider
range of gravitational waves to be detected. LISA is now defunct, but
the idea was resurrected in a new project called eLisa. For
information see...
The first phase of this project called
eLisa Pathfinder was launched this past December. It is a proof of
concept which will not be able to detect gravitational waves, but
will develop some of the technologies needed to detect gravitational
waves. The current plan is to launch eLisa in the year 2034.
