- 4422
- STARS -
from birth to death? - Hubble Telescope witnesses a new star being
born in a stunning cosmic light show.
The infant star FS Tau B is blasting out a powerful jet of matter that
is slamming into sounding material.
------------------------- 4422
- STARS -
from birth to death?
- The Space Telescope has imaged this
powerful jet erupting from a natal envelope of gas and dust that represents a
newly born star announcing itself to the universe. Hubble spotted the infant star slicing its
way out of the nebula that birthed it when it zoomed in on the youthful
multi-star system FS Tau.
-
- Located 450 light years from Earth, “FS
Tau” is part of the Taurus-Auriga region. This region of space houses a stellar
nursery of dark clouds of gas and dust, or "molecular clouds," that
are home to numerous newly forming protostars and young stars.
-
- Astronomers had previously discovered binary
infant stars in this 2.8 million-year-old nebula, and now a second infant star,
designated “FS Tau B”. Both FS Tau B
and the previously discovered infant stars in the FS Tau stellar nursery, a
binary named FS Tau A (Haro 6-5A), are shrouded in illuminated gas and dust.
This represents what is left of the matter in which overdense patches formed
and collapsed to birth these stars.
-
- As the Hubble image shows FS Tau B is
partially obscured by a dark, vertical lane of dust. This is believed to be the
edge of a pancake-shaped gathering of gas, and dust called a protoplanetary
disk that surrounds the infant star.
This material left over from the formation of FS Tau B will eventually
coalesce to form planets.
-
- FS Tau B isn't a fully-fledged star just
yet. This protostar is currently gathering material from its surroundings. Once
it has accumulated enough mass, the pressure at the heart of FS Tau B will be
so great that hydrogen begins to undergo nuclear fusion to create helium in its
stellar core. That is the nuclear process that defines the main sequence
lifetime of a star.
-
- FS Tau B and similar protostars shine not
because of nuclear fusion but because of the heat generated by the collapse of
the dust cloud that birthed them and from the accretion of more material.
-
- Protostars are known to erupt with
fast-moving columns of highly energetic particles called jets, and FS Tau B is
a prime example of this phenomenon. This particular jet is also remarkable as
it is double-sided yet is also unusually asymmetrical. Seen as a bright blue
streak, the jet's asymmetry could be the result of the star expelling mass at
different rates across its body.
-
- As well as being a protostar, FS Tau B is
classed as a “Herbig-Haro” object. This is a celestial body that is created
when jets ejected from a young star slam into nearby clouds of gas and dust at
high speeds. These impacts result in glowing patches in and around the nebulas
that house protostars.
-
- Once FS Tau B leaves the protostar phase,
it will become a “T Tauri star”, a stellar object on the road to main sequence
status like our 4.6 billion-year-old middle-aged star, the sun.
-
- Exploding stars are rare but emit torrents
of radiation—one close enough to Earth could threaten life on the planet. Stars like the sun are remarkably constant.
They vary in brightness by only 0.1% over years and decades, thanks to the
fusion of hydrogen into helium that powers them. This process will keep the sun
shining steadily for about 5 billion more years, but when stars exhaust their
nuclear fuel, their deaths can lead to pyrotechnics.
-
- The sun will eventually die by growing
large and then condensing into a type of star called a “white dwarf”. But,
stars more than eight times more massive than the sun die violently in an
explosion called a “supernova”.
-
- Supernovae happen across the Milky Way only
a few times a century, and these violent explosions are usually remote enough
that people here on Earth don't notice. For a dying star to have any effect on
life on our planet, it would have to go supernova within 100 light years from
Earth.
-
- Very few stars are massive enough to die in
a supernova. But when one does, it briefly rivals the brightness of billions of
stars. At one supernova per 50 years, and with 100 billion galaxies in the
universe, somewhere in the universe a supernova explodes every hundredth of a
second.
-
- The dying star emits high energy radiation
as gamma rays. Gamma rays are a form of electromagnetic radiation with
wavelengths much shorter than light waves.
They're invisible to the human eye. The dying star also releases a
torrent of high-energy particles in the form of “cosmic rays” which are
subatomic particles moving at close to the speed of light.
-
- Supernovae in the Milky Way are rare, but a
few have been close enough to Earth that historical records discuss them. In
185 A.D., a star appeared in a place where no star had previously been seen. It
was probably a supernova.
-
- Observers around the world saw a bright
star suddenly appear in 1006 A.D.
Astronomers later matched it to a supernova 7,200 light years away.
Then, in 1054 A.D., Chinese astronomers recorded a star visible in the daytime
sky that astronomers subsequently identified as a supernova 6,500 light years
away.
-
- Johannes Kepler observed the last supernova
in the Milky Way in 1604, so in a statistical sense, the next one is overdue.
-
- At 600 light years away, the red supergiant
Betelgeuse in the constellation of Orion is the nearest massive star getting
close to the end of its life. When it goes supernova, it will shine as bright
as the full moon for those watching from Earth, without causing any damage to
life on our planet.
-
- If a star goes supernova close enough to
Earth, the gamma-ray radiation could damage some of the planetary protection
that allows life to thrive on Earth. There's a time delay due to the finite
speed of light. If a supernova goes off 100 light years away, it takes 100
years for us to see it.
-
- Astronomers have found evidence of a
supernova 300 light years away that exploded 2.5 million years ago. Radioactive
atoms trapped in seafloor sediments are the telltale signs of this event.
Radiation from gamma rays eroded the ozone layer, which protects life on Earth
from the sun's harmful radiation. This event would have cooled the climate,
leading to the extinction of some ancient species.
-
- Safety from a supernova comes with greater
distance. Gamma rays and cosmic rays spread out in all directions once emitted
from a supernova, so the fraction that reach the Earth decreases with greater
distance. For example, imagine two identical supernovae, with one 10 times
closer to Earth than the other. Earth would receive radiation that's about a
hundred times stronger from the closer event.
-
- A supernova within 30 light years would be catastrophic,
severely depleting the ozone layer, disrupting the marine food chain and likely
causing mass extinction. Some astronomers guess that nearby supernovae
triggered a series of mass extinctions 360 to 375 million years ago. These
events happen within 30 light years only every few hundred million years.
-
- But supernovae aren't the only events that
emit gamma rays. Neutron star collisions cause high-energy phenomena ranging
from gamma rays to gravitational waves.
Left behind after a supernova explosion, neutron stars are city-size
balls of matter with the density of an atomic nucleus, so 300 trillion times
denser than the sun.
-
- These collisions created many of the gold
and precious metals on Earth. The intense pressure caused by two ultradense
objects colliding forces neutrons into atomic nuclei, which creates heavier
elements such as gold and platinum.
-
- A neutron star collision generates an
intense burst of gamma rays. These gamma rays are concentrated into a narrow
jet of radiation that packs a big punch.
If the Earth were in the line of fire of a gamma-ray burst within 10,000
light years, or 10% of the diameter of the galaxy, the burst would severely
damage the ozone layer. It would also damage the DNA inside organisms' cells,
at a level that would kill many simple life forms like bacteria.
-
- That sounds ominous, but neutron stars do
not typically form in pairs, so there is only one collision in the Milky Way
about every 10,000 years. They are 100 times rarer than supernova explosions.
Across the entire universe, there is a neutron star collision every few
minutes.
-
- Gamma-ray bursts may not hold an imminent
threat to life on Earth, but over very long time scales, bursts will inevitably
hit the Earth. The odds of a gamma-ray burst triggering a mass extinction are
50% in the past 500 million years and 90% in the 4 billion years since there
has been life on Earth.
-
- By that math, it's quite likely that a
gamma-ray burst caused one of the five mass extinctions in the past 500 million
years. Astronomers have argued that a gamma-ray burst caused the first mass
extinction 440 million years ago, when 60% of all marine creatures disappeared.
-
- The most extreme astrophysical events have
a long reach. Astronomers were reminded of this in October, 2022, when a pulse
of radiation swept through the solar system and overloaded all of the gamma-ray
telescopes in space.
-
- It was the brightest gamma-ray burst to
occur since human civilization began. The radiation caused a sudden disturbance
to the Earth's ionosphere, even though the source was an explosion nearly 2
billion light years away. Life on Earth was unaffected, but the fact that it
altered the ionosphere is sobering. A
similar burst in the Milky Way would be a million times brighter.
-
- An international team of astronomers and
astrophysicists has found evidence that the bright gamma-ray burst “GRB
230307A” observed last year was caused by two neutron stars merging, not from a
collapsing massive star.
-
- Prior research has shown that the strongest
occasional flashes of light in the night sky are made by gamma-ray bursts.
There are two basic kinds of GRBs: those that last longer than two seconds and
those that are shorter. Study of these bursts has shown that the shorter bursts
are typically the result of merging neutron stars. Longer bursts, on the other
hand, were believed to occur when a massive star collapses.
-
- Neutron stars are created when massive
supergiant stars collapse during a supernova. Once created, they can wander
aimlessly alone through space. Sometimes, they travel close to another neutron
star, forming a neutron binary system. As they orbit one another, they release
gravitational waves, which can be measured here on Earth.
-
- As they spiral, they are also pulled more
tightly to one another until they eventually merge, emitting a massive burst of
gamma rays, which on Earth looks like a bright burst of light—such bursts are
called kilonovae. In studying GRB 230307A, researchers found that not only had
it had been the source of the second-largest gamma-ray burst ever recorded, but
it was also due to a kilonova, confounding theories regarding how GRBs are
created.
-
- The team studied the events leading up to
the merger, the merger itself, and the material left after the collision—the
first study of its kind. In focusing on the atomic nuclei left behind after the
collision, the researchers found evidence of the creation of several heavy
elements, including gold and silver. Further study of how such elements were
formed, they suggest, could help to better understand how the universe as a
whole was formed.
-
-
April 7, 2023 STARS
- from birth to death? 4422
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------ “Jim Detrick” -----------
--------------------- --- Sunday, April 7, 2024
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