Geminga
Published on Feb 14, 2007 at 1:51 pm.
1 Comment.
Filed under neutron stars.
Located near the foot of Gemini is perhaps the closest neutron star that we know, at only a bit over 500 lightyears away. Discovered by the Small Astronomy Satellite 2 (SAS-2) in the early 1970’s, very little was known about this object other than that it was a gamma ray source. But, the resolution of the satellite was insufficient to identify the exact object causing the gamma rays. It was speculated that a neutron star could do this, but no radio pulses were detected in the area. The name Geminga was given to the unknown object. This name was a contraction of “Gemini gamma ray source.” Interestingly, geminga also means “it is not there” in one Italian dialect.
In 1991, ROSAT detected periodic variations in the X-ray output from Geminga. Finally, HEAO-2 (the Einstein Observatory satellite) identified the source of the mystery gamma ray sources. Geminga has since been studied by the Hubble Space Telescope and the Compton Gamma Ray Observatory. However, it still appears to evade detection by radio astronomers. This makes Geminga a radio quiet pulsar.
The neutron star that is Geminga likely formed in a supernova some 300,000 years ago, and this supernova may have been partially responsible for sweeping out some of the interstellar medium in the part of the galaxy near the Solar System. We call this cavity of high temperature and thin gas that the Sun is embedded in the Local Bubble.
The fact that Geminga is a radio quiet pulsar means that there may be a lot more neutron stars out there that we don’t know about. The easiest way to detect them is by the regular radio pulses that they make. And, that obviously doesn’t work with radio quiet pulsars! So, there may be others even closer that we don’t know about.
-Astroprof
Image credit:Â NASA, XMM
Vic George on August 1, 2009 at 7:28 am: 1
Only when a neutron star is aligned to the Earth with one of the poles is facing us can something be detected. A neutron star’s powerful magnetic field accelerates electrons along the magnetic axis, creating the emission of a beam of electromagnetic radiation rotating with the fast spinning star. This creates a pulse when the beam intercepts our line of sight. Maybe Geminiga’s rotational axis is at 90 degrees to the Earth, hence why it seems to be radio quiet.