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 spectroscopy, spectra showing prominent broad emission lines of ionised helium and highly ionised nitrogen or carbon. The spectra indicate very ...

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 ...

, which is about 6.4 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 first constellati ...

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 Sun's outermost atmospheric layer, the Stellar corona, corona. This Plasma (physics), plasma mostly consists of electrons, protons and alpha particles with kinetic energy betwee ...

and which absorbs much of the star's light. It was discovered by American astronomer Paul W. Merrill in 1938, at the same time that he discovered the star it surrounds. It is approximately 6 light years 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 (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...

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 , and the mass of its ionised gas is estimated at . The morphology of M1-67 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, bow shocks are shock waves in regions where the conditions of density and pressure change dramatically due to blowing stellar wind. Bow shock occurs when the magnetosphere of an astrophysical object interacts with the nearby fl ...

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 A year is a unit of time based on how long it takes the Earth to orbit the Sun. In scientific use, the tropical year (approximately 365 solar days, 5 hours, 48 minutes, 45 seconds) and the sidereal year (about 20 minutes longer) are more exa ...

. 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 im ...

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