WHAT'S NEW SINCE PUBLICATION:
Stars and Stellar Evolution

Jon Morse (University of Colorado) and NASA
- It appears that isolated stellar-mass black holes have been detected,
using the Hubble Space Telescope.
The detections were made by observing the effects of gravitational lensing
on distant background stars and announced at the January 2000 meeting
of the American Astronomical Society. The Space Telescope Science
Institute provided a press
release on January 13, 2000.
- Thanks to spectacular new images
and other data from spacecraft such as Yohkoh,
TRACE, Ulysses, and SOHO, along with ground-based observations, we
are gaining new insights into the nature of the Sun, including solar oscillations, magnetic fields (MHD), flares, prominences,
and other solar activity.
- The spectacular image shown above may not be material ejected from the luminous star Eta
Carinae. According to a result published in the Astrophysical Journal Letters,
505, L131-133, October 1, 1998, Lamers, Livio, Panagia,
and Walborn argue that the nebula is more chemically advanced (metal-rich) than the
central star. It appears that Eta Carinae may be part of a binary star system with a
period of 5.5 years. The unseen companion must be more evolved than Eta Carinae
itself.
- Evidence is growing that a new class of ultra-strong magnetic field stars, magnetars,
may exist. These stars may possess field strengths of >1014 G.
One possible candidate for a magnetar is SGR 1900 +14, which sent a stream of gamma rays
through the Solar System on August 27, 1998. The activity was
detected by several space craft, including Ulysses.
See Science News, September 12,
1998.
- A new spectral class (L) has been recently been suggested that would extend the
well-known spectral classification scheme, OBAFGKM (see An Introduction to Modern
Astrophysics, p. 223). Using the Keck
II Telescope, stars cooler than class M have been discovered with atmospheres
containing appreciable quantities of iron hydride and chromium hydride. To date, ten
of these very cool, very low-mass stars have been detected (and are distinct from brown
dwarfs). If the new class becomes established, the classification scheme would then
be OBAFGKML (with the possible mnemonic: "Oh be a Fine Girl/Guy, Kiss My
Lips"). See Science News, July
4, 1998.
- Neutrino oscillations have been verified at the Super-Kamiokande laboratory in Japan and
were announced June 5, 1998 at the Neutrino '98 Conference in Takayama,
Japan. These results imply a small but non-zero rest mass for neutrinos (estimated
to be 0.07 +/- 0.04 eV). This discovery could have profound implications for the
solution of the solar neutrino problem (discussed in Section 11.1), the mechanisms for
supernova production, dark matter, and the predominance of matter over anti-matter in the
universe. For more information see http://www.phys.hawaii.edu/~superk; see
also Sky and Telescope, September,
1998, p. 19.
- On December 14, 1997, a gamma-ray burst was detected that appears to
have released 100 times more energy than a supernova explosion. On May 5,
1998 a radio burst was detected from a different part of the sky that also
suggests a supernova explosion with 100 times more energy than is typical. Dubbed
"hypernovae," these events might represent the link between supernovae
and gamma-ray bursts. It may be that typical supernovae yield neutron stars, while
hypernovae produce black holes. For more information, see Science News, May 9, 1998 and May 23, 1998;
see also Sky and Telescope, September,
1998, p. 24.
- The infrared camera, NICMOS, on board the Hubble
Space Telescope, may have imaged an extrasolar
protoplanet for the first time. Located in the constellation of Taurus, the
planet appears to be escaping from a newborn binary star system. Given the low
luminosity of the object, it is unlikely to be a dim star, but a planet having a mass of
several Jupiters. The announcement of the detection was released on May 28,
1998.
- Tornados have been discovered on the surface of the Sun by the SOHO spacecraft.
The announcement was made on April 28, 1998. These solar tornadoes,
which can be larger than the entire earth, are likely to provide important information
about the solar wind and the solar corona.
- In April 1998, the Space
Telescope Science Institute announced that Hubble has recently identified a very
young, hot white dwarf that was formed from a 7.6 solar mass progenitor.
This places a new lower limit on the mass of main-sequence stars that will form
white dwarfs rather than detonating as a supernovae. The white dwarf was discovered
in the stellar cluster NGC 1818, which is a member of the Large Magellanic Cloud.
Details of the discovery are scheduled to be published in the Astrophysical Journal Letters.
- The latest information about the immediate surroundings of the Crab pulsar
(Section 15.7, p. 616) may be found at the Space
Telescope Science Institute. The right-hand frame of this image shows wisps that move away from the pulsar with a
speed of 0.5c. The pulsar itself is the left of the pair of stars near the center
of the frame. This view was obtained by the HST and was released in May 1996.
[Courtesy of Jeff Hester and Paul Scowen (Arizona State University), and NASA.]
- The existence of a brown dwarf has been confirmed. Gliese 229B has a mass of
between 20 and 50 Jupiter masses (the lower limit for nuclear fusion is about 80 Jupiter
masses). It was discovered by Tadashi Nakajima (Caltech) and colleagues at Mount Palomar
and confirmed by the Hubble Space Telescope. This discovery makes the comment in footnote
6 of Chapter 20 (p. 826) out of date! (Refs: Sky and
Telescope, January 1996, p. 11, and June 1996, p. 24.)
- An image of new-born stars emerging from globules in
the Eagle Nebula (M16) was obtained by the Hubble
Space Telescope and released to the public in November 1995. The EGGs (evaporating
gaseous globules) of M16 are located in Serpens, approximately 2000 pc away. For
background on the interstellar medium, star formation, and HII regions, see Chapter 12.
[Courtesy of Jeff Hester and Paul Scowen (Arizona State University), and NASA.]
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Last modified September 12, 2005.