[Music]
[Music] Narrator: Eta Carinae
is the most massive star within 10,000 light-years.
In the mid-nineteenth century, a tremendous eruption hurled
enough gas into space to make at least 10 copies of the sun, creating
an expanding nebula still visible today. New results from
NASA satellites, ground-based telescopes, and theoretical models are
providing astronomers with an improved understanding of the system.
At the nebula's heart lie two giant stars. The smaller of the two
is 30 times the mass of the sun and a million times brighter.
The primary weighs 90 suns and shines 5 times brighter than
its companion. Both stars produce powerful outflows called
stellar winds, but the primary's is so dense it prevents astronomers
from directly observing the star. The secondary's orbit
is among the most eccentric known. Every five and a half years, when the
two stars swing toward closest approach, or periastron, the come about
as close to each other as Mars is from the sun.
Eta Carinae's most recent periastron occurred in August 2014,
and many of NASA's space-based telescopes, as well as ground-based
observatories, looked on. Where the stellar winds collide,
temperatures reach hundreds of degrees - hot enough to emit
X-rays. But the X-ray emission shuts down near periastron,
when the smaller star is swallowed up by the dense wind of its larger companion.
The X-rays gradually recover after periastron,
but they do so a bit differently each time, suggesting structural
changes in the dueling winds. Recent observations have
helped theorists refine computer models of this interaction. Here,
darker colors indicate lower gas densities around the stars,
while the stars themselves appear as black circles. When the stars are
far apart, the winds collide head-on, creating a huge cavity
surrounded by 50-million-degree gas. But near periastron,
the secondary whips around the larger star, carving a tunnel though the primary's
dense wind. The secondary star's rapid motion changes the
collision zone from head...to tail. The smaller star's
faster wind flows out along the cavity it created and then crashes into the
outward-moving wind of its companion. From out perspective on Earth,
the X-rays fade, then recover, as the stars move apart.
New 3-D models of these simulations reveal the formation
of finger-like protrusions along the cavity near periastron,
features never before identified. Theorists now investigating
the phenomenon suggest they may arise from instabilities developing in gas as
it flows along the cavity wall. Astronomers also
keep an eye on Eta Carinae with the Hubble Space Telescope.
These images show a structure resembling a crab, formed by gas
excited by the secondary star's intense UV light.
This light dims near periastron, when the secondary passes through the thickest part of
the primary's wind. The gas relaxes, settling into a lower-energy state.
As a result, the crab appears in a different
spectral line until the stars move apart and the UV light is restored.
Eta Carinae is one of the closest and most
massive colliding-wind binaries, and serves as a natural laboratory for
studying these rare and important objects. While its past
eruptions remain unexplained, astronomers think they have a handle on its current
state--a claim to be tested at the next periastron in February
2020. [Music]
[Beeping]