Stories from Physics for 11-14 14-16
- During the initial collapse of a nebula into a protostar, the temperature of the collapsing material is low, typically around 30 K. During this stage, the protostar may occupy a sphere with a radius of around 1000 astronomical units (one astronomical unit is approximately the distance from the Earth to the Sun which equates to about 200 times the distance to Pluto at its furthest from the Sun).The protostar remains shrouded in a cloud of dust and gas and only radio emissions are detectable from this phase of its development.
As the protostar collapses, it develops a magnetic field which increases in intensity as the star’s size decreases. Observations from satellite X-ray observatories have detected unexpectedly intense X-ray radiation emanating from cold protostars. It is speculated that the magnetic fields of protostars accelerate matter to high velocities (up to 2000 km/s). When the accelerated material collides with the protostar, X-rays are emitted. The process that generates the magnetic fields is still the subject of speculation – one explanation is a dynamo-effect-like process.
- Protostars can fire out jets of material: in 2011, data collected by the European Space Agency’s Herschel Space Observatory showed evidence of a protostar, dubbed the ‘stellar sprinkler’, emitting jets of hydrogen and oxygen at velocities of 200,000 km/hr.
- Astrophysicists have recently succeeded in imaging a dusty accretion disc that surrounds a very young protostar. They describe the disc as having a ‘hamburger-shaped’ appearance. HH 212, a very young protostar (around 40,000 years old) in the constellation of Orion, has in addition to an equatorial disc, two powerful jets of materials emanating from its poles.