Hubble Space Telescope finds source of Magellanic Stream

New observations reveal most of the gas was stripped from the Small Magellanic Cloud about 2
billion years ago, and a second region of the stream originated more recently from the Large
Magellanic Cloud.
By STScl, Baltimore, Maryland, NASA Headquarters, Washington, D.C. — Published: August 9, 2013

All-sky view of the Magellanic Stream (radio/visible-light). // D. Nidever et al., NRAO/AUI/NSF and A.
Mellinger, Leiden-Argentine-Bonn (LAB) Survey, Parkes Observatory, Westerbork Observatory, and
Arecibo Observatory
Astronomers using NASA’s Hubble Space Telescope have solved a 40-year mystery on the origin of
the Magellanic Stream, a long ribbon of gas stretching nearly halfway around our Milky Way Galaxy.

The Large and Small Magellanic Clouds, two dwarf galaxies orbiting the Milky Way, are at the head
of the gaseous stream. Since the stream’s discovery by radio telescopes in the early 1970s,
astronomers have wondered whether the gas comes from one or both of the satellite galaxies. New
Hubble observations reveal most of the gas was stripped from the Small Magellanic Cloud about 2
billion years ago, and a second region of the stream originated more recently from the Large
Magellanic Cloud.

A team of astronomers, led by Andrew J. Fox of the Space Telescope Science Institute in Baltimore,
determined the source of the gas filament by using Hubble’s Cosmic Origins Spectrograph to
measure the amount of heavy elements, such as oxygen and sulfur, at six locations along the
Magellanic Stream. They observed faraway quasars, the brilliant cores of active galaxies that emit
light that passes through the stream. They detected the heavy elements from the way the elements
absorb ultraviolet light.

Fox’s team found a low amount of oxygen and sulfur along most of the stream, matching the levels
in the Small Magellanic Cloud about 2 billion years ago, when the gaseous ribbon is thought to have
formed. In a surprising twist, the team discovered a much higher level of sulfur in a region of the
stream that is closer to the Magellanic Clouds.

“We’re finding a consistent amount of heavy elements in the stream until we get very close to the
Magellanic Clouds, and then the heavy element levels go up,” said Fox. “This inner region is very
similar in composition to the Large Magellanic Cloud, suggesting it was ripped out of that galaxy
more recently.”

“Only Hubble can measure these abundances,” Fox said. “These abundances can only be
measured in ultraviolet light, which Earth’s atmosphere absorbs, and so the observations can only
be done from a telescope in space.”

Unlike other satellite galaxies of the Milky Way, the Magellanic Clouds have been able to retain their
gas and still form stars because they’re more massive than the other satellites. However, as they’re
now approaching the Milky Way, they’re feeling its gravity more and also encountering its halo of
hot gas, which pushes their own gas out. That process, together with the gravitational tug-of-war
between the Magellanic Clouds, leads to the production of a stream.

Ultimately, the gaseous stream may rain down onto the Milky Way’s disk, fueling the birth of new
stars. This infusion of fresh gas is part of a process that triggers star formation in a galaxy.
Astronomers want to know the origin of that wayward gas in order to more fully understand how
galaxies make new stars.

“We want to understand how galaxies like the Milky Way strip the gas from small galaxies that fall
into them and then use it to form new stars,” Fox said. “This seems like it’s an episodic process. It’s
not a smooth process where a slow stream of gas comes in continuously. Instead, once in a while a
large gas cloud falls in. We have a way of testing that here,where two galaxies are coming in. We’ve
shown which of them is producing the gas that ultimately will fall into the Milky Way.”

From The Urantia Book (copyright 1955)
15:4.8   The Milky Way galaxy is composed of vast numbers of former spiral and other nebulae, and
many still retain their original configuration. But as the result of internal catastrophes and external
attraction, many have suffered such distortion and rearrangement as to cause these enormous
aggregations to appear as gigantic luminous masses of blazing suns, like the Magellanic Cloud. The
globular type of star clusters predominates near the outer margins of Orvonton.

15:3.6   The nucleus of the physical system to which your sun and its associated planets belong is
the center of the onetime Andronover nebula. This former spiral nebula was slightly distorted by the
gravity disruptions associated with the events which were attendant upon the birth of your solar
system, and which were occasioned by the near approach of a large neighboring nebula. This near
collision changed Andronover into a somewhat globular aggregation but did not wholly destroy the
two-way procession of the suns and their associated physical groups. Your solar system now
occupies a fairly central position in one of the arms of this distorted spiral, situated about halfway
from the center out towards the edge of the star stream.

57:4.1   The primary stage of a nebula is circular; the secondary, spiral; the tertiary stage is that of
the first sun dispersion, while the quartan embraces the second and last cycle of sun dispersion,
with the mother nucleus ending either as a globular cluster or as a solitary sun functioning as the
center of a terminal solar system.