Mz 3

Mz 3 (Menzel 3) is a young bipolar planetary nebula (PN) that is composed of a bright core and four distinct high-velocity outflows that have been name lobes, columns, rays, and chakram. These nebulosities are described as: two spherical bipolar lobes, two outer large filamentary hour-glass shaped columns, two cone shaped rays, and a planar radially expanding, elliptically shaped chakram.^[4][5] A complex system composed of three nested pairs of bipolar lobes and an equatorial ellipse, Mz 3 is perhaps one of the most stunning bipolar PN known.^[6] Its lobes all share the same axis of symmetry but each have very different morphologies and opening angles.^[6] It is an unusual PN in that it is believed, by some researchers, to contain a symbiotic binary at its center.^[5] Study suggests that the dense nebular gas at its center may have originated from a source different than that of its extended lobes.^[5] The working model to explain this hypothesizes that this PN is composed of a giant companion that caused a central dense gas region to form, and a white dwarf that provides ionizing photons for the PN.^[5]

Mz 3 is often referred to as the Ant Nebula because it resembles the head and thorax of a garden-variety ant.

Characteristics

Mz 3 is radially expanding at a rate of about 50 km/s and has its polar axis oriented at an angle of around 30° from the plane of the sky (Lopez & Meaburn 1983; Meaburn & Walsh 1985). It is sometimes compared to the more extensively studied Butterfly Nebula (M 2-9), and it is quite likely that both have a similar evolutionary history. They both have point-like bright nuclei, are narrow-waisted bipolar nebulae, and share surprisingly similar spatially dependent spectra. Because of their similarity, their differences are note worthy. Their greatest difference is probably in their near infrared emissions. Mz 3 has no trace of molecular hydrogen emission, whereas the M 2-9 has prominent H₂ emission lines in the near-IR. The lack of H₂ emissions from Mz 3 is unusual given the strong correlation between such emissions and bipolar structures of PN. Additionally, the polar lobes of Mz 3 are more mottled and rounded as compared to M 2-9. Finally, Mz 3 is not known to evidence temporal variability in its polar lobes as is found in M 2-9 (Doyle et al. 2000). (Smith 2003)

Chakram

Of the morphological features of Mz 3, one of the most unusual and odd is the chakram (first noticed in 2004), a faint, large, limb brightened ellipse that appears to have its center on the PN's nucleus. While the plane of the ellipse is near the other feature's shared reflection symmetry plane, it is definitely offset. This structure's kinematics are the only such ones known among studied PN. Unlike all the other Mz 3 structures, there is no increase of velocity as the radial offset from the nucleus increases. Consequently, this must not be a simple equatorial flow despite the fact that its motion appears to be strictly radial (that is, there is no indication of rotation which would suggest that this feature is dynamically stable). All the kinematic properties of the ellipse are symmetric and very ordered relative to the nucleus, consistent with all the other Mz 3 features. Therefore, the ellipse must be historically linked to the evolution of the central star. (Santander-García et al. 2004)

History

Mz 3 was discovered by Donald Howard Menzel in 1922.^[2] Menzel 1922

It was studied on July 20, 1997 by astronomers Bruce Balick (University of Washington) and Vincent Icke (Leiden University) on observations done with the Hubble Space Telescope. The telescope was later used on June 30, 1998 by Raghvendra Sahai and John Trauger of the Jet Propulsion Laboratory to picture the PN.

nebula

A nebula (from Latin: "cloud" [1]; pl. nebulae or nebulæ, with ligature or nebulas) is an interstellar cloud of dust, hydrogen gas and plasma. Originally nebula was a general name for any extended astronomical object, including galaxies beyond the Milky Way (some examples of the older usage survive; for example, the Andromeda Galaxy was referred to as the Andromeda Nebula before galaxies were discovered by Edwin Hubble). Nebulae often form star-forming regions, such as in the Eagle Nebula. This nebula is depicted in one of NASA's most famous images, the "Pillars of Creation". In these regions the formations of gas, dust and other materials 'clump' together to form larger masses, which attract further matter, and eventually will become big enough to form stars. The remaining materials are then believed to form planets, and other planetary system objects.

Formation

NGC 2024, The Flame Nebula

Many nebulae form from the gravitational collapse of gas in the interstellar medium or ISM. As the material collapses under its own weight, massive stars may form in the center, and their ultraviolet radiation ionises the surrounding gas, which creates plasma (the 4th state of matter), making it visible at optical wavelengths. An example of this type of nebula is the Rosette Nebula or the Pelican Nebula. The size of these nebulae, known as HII regions, varies depending on the size of the original cloud of gas, and the number of stars formed can vary too. As the sites of star formation, the formed stars are sometimes known as a young, loose cluster.

Some nebulae are formed as the result of supernova explosions, the death throes of massive, short-lived stars. The material thrown off from the supernova explosion is ionized by the supernova remnant. One of the best examples of this is the Crab Nebula, in Taurus. It is the result of a recorded supernova, SN 1054, in the year 1054 and at the centre of the nebula is a neutron star, created during the explosion.

Other nebulae may form as planetary nebulae. This is the final stage of a low-mass star's life, like Earth's Sun. Stars with a mass up to 8-10 solar masses evolve into red giants and slowly lose their outer layers during pulsations in their atmospheres. When a star has lost a sufficient amount of material, its temperature increases and the ultraviolet radiation it emits is capable of ionizing the surrounding nebula that it has thrown off.

[edit] Diffuse nebulae

The Omega Nebula, an example of an emission nebula.

The Pleiades. The diffuse nebulae near the stars are examples of reflection nebula.

Most nebulae can be described as diffuse nebulae, which means that they are extended and contain no well-defined boundaries.^[1] In visible light these nebulae may be divided into emission nebulae and reflection nebulae, a categorization that depends on how the light we see is created. Emission nebulae contain ionized gas (mostly ionized hydrogen) that produces spectral line emission.^[2] These emission nebulae are often called HII regions; the term "HII" is used in professional astronomy to refer to ionized hydrogen. In contrast to emission nebulae, reflection nebulae do not produce significant amounts of visible light by themselves but instead reflect light from nearby stars.^[2]

The Horsehead Nebula, an example of a dark nebula.

Dark nebulae are similar to diffuse nebulae, but they are not seen by their emitted or reflected light. Instead, they are seen as dark clouds in front of more distant stars or in front of emission nebulae.^[2]

Although these nebulae appear different at optical wavelengths, they all appear to be bright sources of emission at infrared wavelengths. This emission comes primarily from the dust within the nebulae.^[2]

[edit] Specific types of nebulae

While diffuse nebulae have poorly-defined boundaries, a few nebulae may actually be described as discrete objects with identifiable boundaries.

[edit] Planetary nebulae

The Cat's Eye Nebula, an example of a planetary nebula.

Planetary nebulae are nebulae that form from the gaseous shells that are ejected from low-mass asymptotic giant branch stars when they transform into white dwarfs.^[2] These nebulae are emission nebulae with spectral emission that is similar to the emission nebulae found in star formation regions.^[2] Technically, they are a type of HII region because the majority of hydrogen will be ionised. However, planetary nebulae are denser and more compact than the emission nebulae in star formation regions.^[2] Planetary nebulae are so called because the first astronomers who observed these objects thought that the nebulae resembled the disks of planets, although they are not at all related to planets.^[3]

[edit] Protoplanetary nebula

The Red Rectangle Nebula, an example of a protoplanetary nebula.

A protoplanetary nebula (PPN) is an astronomical object which is at the short-lived episode during a star's rapid stellar evolution between the late asymptotic giant branch (LAGB) phase and the subsequent planetary nebula (PN) phase.^[4] A PPN emits strong in infrared radiation, and is a kind of reflection nebula. The exact point when a PPN becomes a planetary nebula (PN) is defined by the temperature of the central star.

[edit] Supernova remnants

The Crab Nebula, an example of a supernova remnant.

A supernova occurs when a high-mass star reaches the end of its life. When nuclear fusion ceases in the core of the star, the star collapses inward on itself. The gas falling inward either rebounds or gets so strongly heated that it expands outwards from the core, thus causing the star to explode.^[2] The expanding shell of gas form a supernova remnant, a special type of diffuse nebula.^[2] Although much of the optical and X-ray emission from supernova remnants originates from ionized gas, a substantial amount of the radio emission is a form of non-thermal emission called synchrotron emission.^[2] This emission originates from high-velocity and electrons oscillating within magnetic fields.