M1-67 is an ejecta nebula that surrounds the

Wolf–Rayet star Wolf–Rayet stars, often abbreviated as WR stars, are a rare heterogeneous set of stars with unusual spectra showing prominent broad emission lines of ionised helium and highly ionised nitrogen or carbon. The spectra indicate very high surface ...

WR 124 WR 124 is a Wolf–Rayet star in the constellation of Sagitta surrounded by a ring nebula of expelled material known as M1-67. It is one of the fastest runaway stars in the Milky Way with a radial velocity around . It was discovered by Pau ...

, which is about 5.87 kpc from Earth in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Sagitta Sagitta is a dim but distinctive constellation in the northern sky. Its name is Latin for 'arrow', not to be confused with the significantly larger constellation Sagittarius 'the archer'. It was included among the 48 constellations listed by t ...

. It contains dust which is caught up in WR 124's

solar wind The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sola ...

and which absorbs much of the star's light. It was discovered by American astronomer

Paul W. Merrill Paul Willard Merrill (August 15, 1887 – July 19, 1961) was an American astronomer whose specialty was spectroscopy. He was the first to define S-type stars in 1922. Career He received his Ph.D. at the University of California (now UC Berkeley) ...

in 1938, at the same time that he discovered the star it surrounds. It is approximately 6 lightyears across, making it about 20,000 years old.

Distance and characteristics

A 2010 study focused on M1-67, measuring its expansion rate by using

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...

photographs taken 11 years apart. The expansion rate was then compared to the expansion velocity, which was calculated from the Doppler shift of its nebular emission lines, resulting in a geometric distance of d=3.35 ± 0.67kpc. NASA has confirmed that the released gas is traveling at up to 100,000 mp/h, causing turbulence, and carrying along approximately 100 billion-mile wide glowing blobs, with each blob being around 30 times the mass of the Earth. The blast took place around 10,000 years or 10 millennia ago. An infrared study of the nebula showed that it consists of mildly processed material with number ratios of N/O = 1.0 ± 0.5 and C/O = 0.46 ± 0.27. The mass of the nebula's dust has been confirmed to be . The morphology of M-167 is complex and knotted, unlike other Wolf–Rayet nebulae. Studying the dynamics of the nebula has suggested that it has interacted with the surrounding ISM, causing a

bow shock In astrophysics, a bow shock occurs when the magnetosphere of an astrophysical object interacts with the nearby flowing ambient plasma such as the solar wind. For Earth and other magnetized planets, it is the boundary at which the speed of ...

which travels at a high velocity of about 180 km/s. WR 124 is determined to be about 1.3 parsecs away from the bow shock. The wind collided with the bow shock shortly after the outburst, oriented along its main axis, as evidenced by the lack of emission found within the radial velocities in the centre of the nebula as seen from telescopes on Earth. Higher radial velocities were found in the center and lower velocities near the edge, giving an estimated expansion rate of 150 km/s and dynamical timescales of 8 to 20

kyr The abbreviation kyr means "thousand years". kyr was formerly common in some English language works, especially in geology and astronomy, for the unit of 1,000 years or millennium. The "k" is the unit prefix for kilo- or thousand with the suffix ...

. However, there are other explanations for its shape that do not require a bow shock. An alternative model suggest that WR 124 is a

bipolar nebula A bipolar nebula is a type of nebula characterized by two lobes either side of a central star. About 10-20% of planetary nebulae are bipolar. Formation Though the exact causes of this nebular structure are not known, it is often thought to impl ...

with its axis in pointing northwest, surrounded by an equatorial torus, as well as jets expanding in the eastern direction.

References

{{Sky, 19, 11, 30.875, +, 16, 51, 38.199 Planetary nebulae Sagitta Astronomical objects discovered in 1938