Hubble catches a cosmic 'bubble'
The latest image of the Bubble Nebula
January 18, 2000
Web posted at: 9:49 AM EST (1449 GMT)
(CNN) -- NASA's Hubble Space Telescope has taken pictures of
the Bubble Nebula with unprecedented clarity, helping
astronomers understand for the first time the geometry and
dynamics of the enigmatic system, the Space Telescope Science
Institute said in a statement.
The remarkably spherical "bubble" marks the boundary between
an intense wind of particles from a massive central star and
the more quiescent interior of the nebula, astronomers said.
The star of the nebula has 40 times more mass than the sun
and is responsible for a stellar wind moving at 4 million mph
(7 million km/h), which propels particles off the surface of
The bubble surface actually marks the leading edge of this
wind's gust front, which is slowing as it plows into the
denser surrounding material. The surface of the bubble is not
uniform because as the shell expands outward it encounters
regions of the cold gas, which with varying densities slow
the expansion by differing amounts, resulting in the rippled
It is this gradient of background material that the wind is
encountering that places the central star off center in the
bubble. There is more material to the northeast of the nebula
than to the southwest, so that the wind advances less in that
direction, offsetting the central star from the geometric
center of the bubble.
The Bubble Nebula is located 7,100 light-years from Earth in the constellation Cassiopeia. It has a diameter of 6 light-years. Scientists refer to the nebula as NGC 7635.
The region between the star and ridge reveals several loops
and arcs that have never been seen before. The
high-resolution capabilities of Hubble make it possible to examine
these features in detail in a way that is not possible from
A lower ridge appears to lie within the sphere of the bubble
but is not actually inside the gaseous region. Instead, it is
being pushed up against the bubble like a hand being pushed
against the outside of a party balloon, according to Hubble astronomers.
As the bubble moves up but not through the ridge, bright blue
arcs form where the supersonic wind strikes the ridge.
Scientists say the origin of this "bubble-within-a-bubble" remains unknown. It may be due to a collision of two distinct winds. The
stellar wind may be colliding with material streaming off the
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Hubble Space Telescope
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