One in every of solely 4 planetary nebulae to be included in Charles Messier’s well-known catalogue, fabulous Messier 76 (NGC 650/651) in Perseus rewards observers and imagers alike with its dramatic two-loop or -lobe look, which sufficiently resembles that of summer time’s well-known Dumbbell Nebula (Messier 27) in Vulpecula for it to go by the nickname the ‘Little Dumbbell’. Whereas M76 is a good bit fainter and smaller than M27, and has an unwelcome however well-deserved repute as one of many hardest objects in Messier’s listing to watch, a small telescope will establish it and telescopes within the 200–250mm (eight- to ten-inch) class can begin to outline and element its distinctive form and nebulosity.
Messier 76 is a wonderful and dramatic trying planetary nebula dwelling within the magnificent, far-northern constellation of Perseus. Planetary nebulae are the short-lived end-point within the lives of Solar-like stars, their outer layers expelled with the new core uncovered as an ever-cooling white dwarf remnant, its robust ultraviolet radiation ionising the tenuous surrounding envelope and producing an unbelievable number of lovely nebulae.
M76’s hourglass determine
Messier 76 displays a outstanding bi-polar construction in deep pictures, a central, brighter space that has been variously coined a ‘field’, a ‘cork’ or an ‘hourglass’, with two nebulous loops or lobes. One may liken it to a barred spiral galaxy with a whopping central bar with the spiral arms wrapping round it from both finish; no signal right here of a M57-like ring construction. In lots of respects that is the enjoyment of planetary nebulae, the distinctiveness of every of those objects, with their inherent intricate constructions carved out by the interactions of the expelled outer layers of the dying star throughout its crimson big part with faster-moving, extra not too long ago ejected materials ploughing into it, producing a sequence of shock waves.
M76’s look is one thing of an phantasm brought on by its orientation to Earth; the galaxy analogy is related once more, as we see some galaxies face-on, some inclined to our line-of-sight, to these spectacularly showing edge-on. We see the Little Dumbbell from the aspect, taking a look at its equator (the angle is 75 levels); if we may look proper down the centre of one of many lobes, it might seem like a hoop, as is the case with Messier 57. Astronomers have decided that the north-western lobe is pointing our manner and the central ‘cork’ is increasing at round 45 km/s.
It unsure how distant M76 is and due to this fact how huge it’s. Distances starting from 2,500 to 12,000 mild years are quoted within the literature, however a price of 4,000 mild years is probably going, with the nebula spanning about three mild years. The central star, a white dwarf remnant, may very well be as sizzling as 140,000 levels Celsius and in 1973 is was found to have a companion star a mere 1.4 arcseconds away, equating to between 16,000 to twenty,000 mild years. The companion was itself found to be double in 1995 following Hubble observations, however its now unsure whether or not the pair are bodily associated to the white dwarf.
M76 was found by Pierre Mechain in 1780 and 7 years later William Herschel noticed it together with his a lot bigger telescope. Herschel noticed the 2 lobes and mistook them for 2 separate objects, which accounts for the double NGC numbers 650 and 651 assigned to the Little Dumbbell. In 1891 Isaac Roberts was the primary to provide photographic proof of the nebula’s true nature. Like all planetaries, M76 is transient, its destiny being to regularly disperse into the interstellar medium over the subsequent a number of thousand years.
How one can observe
Messier 76 lies within the very good late-autumn/early-winter constellation of Perseus, which has the winter Milky Method flowing via it and comprises a handful of very good open clusters and nebulae, together with the magnificent Double Cluster. M76 will be present in Perseus’ excessive north-western reaches, near its boundaries with Andromeda and Cassiopeia. It lies roughly halfway between the magnitude +2.1 stars gamma (γ) Cassiopeiae and gamma Andromedae, the latter being a marvellous colour-contrast double star. Zooming in a bit, magnitude +4 phi (φ) Persei lies slightly below a level to the south-south-east. M76 is circumpolar (by no means setting) from the UK and peaks proper on the zenith at about 11pm GMT on the finish of October/begin of November (British Summer time Instances (BST) ends at 2am BST on 30 October).
Though catalogued as magnitude +10.4, and spanning 163” x 107” in obvious diameter, many observers discover M76 to be a neater goal to seek out and observe than its magnitude suggests. In the event you’re on the lookout for it on a really clear and moonless night time at a darkish countryside web site, attempt sweeping with a pair of 10 x 50 binoculars; in any other case an 80mm (~three inches) telescope ought to bag it. In the event you don’t see it at first, attempt the neat trick of utilizing averted imaginative and prescient and improve the magnification (which will increase distinction too). Neil Bone, our much-missed colleague, reported that M76 was seen at 40x however not at 20x via his 80mm telescope and that it appeared to ‘blink’ when he switched between regular and averted imaginative and prescient.
M76 responds properly to narrowband filters – good outcomes will probably be had with both an Extremely Excessive Distinction (UHC) or an Oxygen III (O-III) filter, which passes solely the sunshine of doubly ionised oxygen, M76’s dominant emission.
A moderate- to large-aperture telescope, say from 200mm to 300mm (12-inches) in dimension, can reveal M76’s internal hourglass or dumbbell form, with most observers ranking the south-western lobe, seen maybe within the type of a semicircular arc, which ace American visible observer Stephen James O’Meara describes as a butterfly wing, as brighter and higher outlined than its north-eastern counterpart. How do you see it?
Each lobes are embedded in a fainter, enveloping halo and the nebula’s general form could be very pleasing and photogenic, significantly in deep novice pictures.