Such age calculation methods do not yield stellar ages older than about 15 billion years, perhaps because this is when a solar type main-sequence star
becomes a red giant.
are all powered by hydrogen fusion in their cores; they're fusing four hydrogen atoms to produce a single atom of helium, and releasing a huge amount of energy in the process.
The third type of potential donor in an AM CVn system is the evolved main-sequence star
Either the star is so young that it hasn't finished contracting or so old--about 500 million years--that it has had time to expand its girth after becoming a main-sequence star
In both cases, they're a mix of nearby main-sequence stars
with a handful of more distant giants, scattered over several hundred light-years along our line of sight.
The new observation also marks the first time astronomers have imaged a disk around a mature, main-sequence star
using the radio energy given off by dust particles.
The secondary is usually a late-type main-sequence star
On April 11th, he found WD 1145 undergoing dimmings that looked similar to cases where a transiting planet sheds material if it orbits too close to a normal, much larger main-sequence star
Composed of a white dwarf and a main-sequence star
, the system boasts a massive planet closely orbiting the star.
While the primary is on its way to white-dwarfhood, the companion is a main-sequence star
fusing hydrogen in its core, as does our Sun.
That leaves a main-sequence star
, or perhaps a mildly evolved subgiant, as the white dwarf's feeder object--a valuable data point for sorting out what actually happens in these crucial explosions (S&T: November 2011, page 14).
A main-sequence star
works around the clock fusing hydrogen into heavier elements.