Two of NASA's great observatories,
the Spitzer and Hubble space telescopes, have teamed up to uncover a
mysterious infant star that behaves like a strobe light. Every 25.34
days, the object, designated LRLL 54361, unleashes a burst of light.
Although a similar phenomenon has been observed in two other young
stellar objects, this is the most powerful such beacon seen to date. The
heart of the fireworks is hidden behind a dense disk and envelope of
dust.
Astronomers propose the light flashes are caused by periodic
interactions between two newly formed stars that are binary, or
gravitationally bound to each other. LRLL 54361 offers insights into the
early stages of star formation when lots of gas and dust is being
rapidly accreted, or pulled together, to form a new binary star.
Astronomers theorize the flashes are caused by material suddenly being
dumped onto the growing stars, known as protostars. A blast of radiation
is unleashed each time the stars get close to each other in their
orbits. This phenomenon, called pulsed accretion, has been seen in later
stages of star birth, but never in such a young system or with such
intensity and regularity.
A sequence of images from the Hubble Space Telescope,
shows a pulse of light emanating from the protostellar object LRLL
54361. Most if not all of this light results from scattering off
circumstellar dust in the protostellar envelope. An apparent edge-on
disk, visible at the center of the object, and three separate structures
are interpreted as outflow cavities. The extent and shape of the
scattered light changes substantially over a 25.3-day period. This is
caused by the propagation of the light pulse through the nebula.
Astronomers propose that the flashes are due to material in a
circumstellar disk suddenly being dumped onto the growing stars and
unleashing a blast of radiation each time the stars get close to each
other in their orbit.
"This protostar has such large brightness variations with a precise
period that it is very difficult to explain," said James Muzerolle of
the Space Telescope Science Institute in Baltimore, Md. His paper
recently was published in the science journal Nature.
Discovered by NASA's Spitzer Space Telescope,
LRLL 54361 is a variable object inside the star-forming region IC 348,
located 950 light-years from Earth. Data from Spitzer revealed the
presence of protostars. Based on statistical analysis, the two stars are
estimated to be no more than a few hundred thousand years old.
The infrared image from the NASA/ESA Hubble Space Telescope at the
top of the page shows an image of protostellar object LRLL 54361 and its
rich cosmic neighbourhood, a region called IC 348. The protostar, which
is the bright object with fan-like beams of light coming from it,
located towards the right of the image, is letting off flashes of light
every 25.3 days.
The Spitzer infrared data, collected repeatedly during a period of
seven years, showed unusual outbursts in the brightness of the suspected
binary protostar. Surprisingly, the outbursts recurred every 25.34
days, which is a very rare phenomenon. Astronomers used NASA's Hubble
Space Telescope to confirm the Spitzer observations and reveal the
detailed stellar structure around LRLL 54361.
Hubble observed two cavities above and below a dusty disk. The
cavities are visible by tracing light scattered off their edges. They
likely were blown out of the surrounding natal envelope of dust and gas
by an outflow launched near the central stars. The disk and the envelope
prevent the suspected binary star pair from being observed directly. By
capturing multiple images over the course of one pulse event, the
Hubble observations uncovered a spectacular movement of light away from
the center of the system, an optical illusion known as a light echo.
Muzerolle and his team hypothesized the pair of stars in the center
of the dust cloud move around each other in a very eccentric orbit. As
the stars approach each other, dust and gas are dragged from the inner
edge of a surrounding disk. The material ultimately crashes onto one or
both stars, which triggers a flash of light that illuminates the
circumstellar dust.
The system is rare because close binaries account for only a few
percent of our galaxy's stellar population. This is likely a brief,
transitory phase in the birth of a star system. Muzerolle's team next
plans to continue monitoring LRLL 54361 using other facilities including
the European Space Agency's Herschel Space Telescope. The team hopes to eventually obtain more direct measurements of the binary star and its orbit.
Journal reference: Nature
Image credits: Credit: NASA, ESA, and J. Muzerolle (STScI)
Source: The Daily Galaxy via NASA's Goddard Space Flight Center
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