The Ant Nebula (Menzel 3 or Mz 3 for short) is a young bipolar planetary nebula about 2 light-years across, which is radially expanding at a rate of about 50 km/s. It is located some 8000 light-years away in the constellation Norma. The name of the nebula — the glowing remains of a dying, Sun-like star — is given because it resembles the head and thorax of an ant.
The nebula has arguably the most complex bipolar morphology, consisting of a bright core, three nested pairs of bipolar lobes and an equatorial ellipse. Its bipolar lobes share the same axis of symmetry but have very different opening angles and morphologies: the innermost pair of bipolar lobes shows closed-lobe morphology, whereas the other two have open lobes with cylindrical and conical shapes, respectively.
The expansion characteristics of the two outer pairs of lobes suggest that they originated in an explosive event, whereas the innermost pair of lobes resulted from the interaction of a fast wind with the surrounding material. The equatorial ellipse is associated with a fast equatorial outflow, which is unique among bipolar nebulae.
The dynamical ages of the different structures in Mz 3 suggest episodic bipolar ejections, and the distinct morphologies and kinematics among these different structures reveal fundamental changes in the system between these episodic ejections.
Though approaching the violence of an explosion, the ejection of gas from the dying star at the center of Mz 3 has intriguing symmetrical patterns unlike the chaotic patterns expected from an ordinary explosion. Why would the gas that is streaming away create an ant-shaped nebula out of a round star?
One possibility is that the central star of Mz 3 has a closely orbiting companion that exerts strong gravitational tidal forces, which shape the outflowing gas. For this to work, the orbiting companion star would have to be close to the dying star. So close that the orbiting companion star wouldn’t be far outside the hugely bloated hulk of the dying star. It’s even possible that the dying star has consumed its companion, which now orbits inside of it.
A second possibility is that, as the dying star spins, its strong magnetic fields are wound up into complex shapes. Charged winds moving at speeds up to 1000 kilometers per second from the star are able to follow the twisted field lines on their way out into space. These dense winds can be rendered visible by ultraviolet light from the hot central star or from highly supersonic collisions with the ambient gas that excites the material into florescence.
The Ant Nebula has no trace of molecular hydrogen emission, which is unusual given the strong correlation between such emissions and bipolar structures of planetary nebulae.
Since the central star appears to be so similar to our own Sun, astronomers hope that increased understanding of the history of this giant space ant can provide useful insight into the likely future of our own Sun and Earth. Our Sun’s fate probably will be more interesting, complex, and striking than astronomers imagined just a few years ago.