#astronomy Get to Know the Ghostly Galaxies of Sagittarius

August 21, 2019 - Comment

We frequently consider Sagittarius as dwelling to 1 galaxy solely — the Milky Approach. However two members of the Native Group and a smattering of fainter galaxies reside right here, too. NGC 6822, a.ok.a. Barnard’s Galaxy, is the most important and best galaxy to see in Sagittarius. It was found by American astronomer E. E.


We frequently consider Sagittarius as dwelling to 1 galaxy solely — the Milky Approach. However two members of the Native Group and a smattering of fainter galaxies reside right here, too.

Nearby dwarf galaxy

NGC 6822, a.ok.a. Barnard’s Galaxy, is the most important and best galaxy to see in Sagittarius. It was found by American astronomer E. E. Barnard in 1884.
DSS2 / STScI / NASA / Aladin Sky Atlas

In terms of observing galaxies, Sagittarius appears an unlikely place to go galaxy-hunting. A lot of the constellation overflows with our personal Milky Approach and its ubiquitous mud clouds that blot extra distant galaxies from view. And but nature offers.

Searching the interstellarum Deep Sky Atlas not too long ago, I stumbled throughout dozens of faint MCG and ESO galaxies within the southern and western realm of the Archer. We’ll go away these for one more day and as an alternative start our unlikely extragalactic journey to 4 brighter targets: NGC 6822, NGC 6835, NGC 6836, and the Sagittarius Dwarf Elliptical Galaxy (Sag DEG).

To be honest, Sag DEG (to not be confused with Sag DIG, a dwarf irregular galaxy) is not instantly seen in a telescope. Regardless of an general magnitude of four.5 and obvious diameter of seven.5°, it is 70,000 light-years distant, situated on the far facet of the our galaxy’s core, and impossibly faint. A lot of the dwarf is superimposed on the Milky Approach’s personal star clouds and tough to tease out even for the professionals. However this 10,000-light-year-wide stellar blob possesses 4 globular clusters, the brightest of which is M54, simply seen at eighth magnitude in a small telescope. M54 resides close to Sag DEG’s heart and will even have been its former core. We’ll deal with it as a stand-in for the galaxy itself.

Galaxy with four tails

Left: An artist’s impression of the Sag DEG (orange clump on the left) orbiting the Milky Approach. Repeated shut encounters with our galaxy have stripped away lots of the dwarf’s stars to create a number of tidal tails or star streams. The galaxy orbits ours in a polar orbit and is without doubt one of the closest recognized, lower than half the gap of the Magellanic Clouds. To not scale. Proper: The globular cluster M53, situated about 88,000 light-years away, belongs to Sag DEG and will lie at its core.
Amanda Smith (Institute of Astronomy, College of Cambridge) (left); Jim Misti (proper)

M54 is a dense ball of stars 12′ (arcminutes) throughout situated 1¾° southwest of Third-magnitude Zeta (ζ) Sagittarii. It is the primary and presumably solely globular cluster reassigned to a unique galaxy after greater than two centuries of citizenship within the Milky Approach. Charles Messier first noticed and cataloged the cluster in 1778. In my 15-inch telescope at 64× it appears to be like small resulting from extinction, however its star-like core blazes brightly. Despite the fact that M54 solely climbs to 13° from my latitude, as soon as I cranked the magnification to 245×, I noticed a good looking mist of faint, barely resolved stars within the cluster’s halo together with two brighter outliers — a ~13.5-magnitude star southeast of the core and a 14th-magnitude star due west. Lots of M54’s stars shine round magnitude 15.

Alive with new star birth

This portrait of Barnard’s Galaxy, also called NGC 6822, reveals a lot of stellar pyrotechnics. Reddish nebulae — a number of of that are seen in beginner telescopes — mark areas of lively star formation, the place younger stars warmth up close by gasoline clouds. The putting bubble-shaped nebula at decrease left is dwelling to a clutch of huge, scorching stars that ship waves of matter smashing into surrounding interstellar materials, producing a glowing construction that seems ring-like from our perspective. Different related ripples of heated matter dot the galaxy. South is as much as match the drawing (beneath).
ESO

If we now slide two fists to the northwest of the Teapot’s deal with we arrive at NGC 6822, a barred irregular galaxy 1.6 million light-years away. Its massive dimension —15.5′ × 13.5′ — and low floor brightness could make it difficult to seek out. Some observers have seen it in apertures as small as four inches. The secret’s to make use of low magnification with a large sufficient subject of view to distinction the ghostly galaxy towards a darkish sky. Slender the sector an excessive amount of and also you may utterly miss it.

Sites of starbirth

I made this sketch of Barnard’s Galaxy (NGC 6822) with a 15-inch Dob and magnifications from 64× to 245×. The star sample — with magnitudes proven — will assist information you to the three H II areas: Hubble I, III; Hubble V;and Hubble X. I discovered it useful to increase two traces from the 11.9 and 9.eight stars to create a parallelogram with the 2 foreground stars seated proper subsequent to Hubble V and Hubble X. South is up.
Bob King

At 64× (1° subject of view) within the 15-inch I might simply make out a big, elongated, amorphous glow like breath on a mirror. A number of vibrant subject stars studded the galaxy’s southern border. If in case you have any issue making out the diffuse patch, roll your eyeball across the subject of view to train averted imaginative and prescient to the max. Doing this, I famous that the broad, north–south oriented core of the thing appeared barely brighter than its edges.

As soon as you have recognized the hub of Barnard’s Galaxy screw on a nebula filter — a UHC, O III, or equal — and search the star-popping H II areas first famous by Edwin Hubble that dot its northern halo. Hubble found 5 star-forming areas within the galaxy; at this time we all know of greater than 150. The westernmost patch, a pair of side-by-side nebulae dubbed Hubble I and III, are faintest at ~14 magnitude and 1.5′ throughout. The duo appeared as a single, misty patch with averted imaginative and prescient aided by an O III filter.

Hubble V is the brightest and visual each with and with out the filter as a 30″ (arcsecond) fuzzball with a compact, star-like condensation at its heart. The easternmost blob, Hubble X, is fainter, smaller (~20″) and extra diffuse with a slight brightening within the core. Like Hubble V, it is also seen with out a nebular filter. Each strongly resemble faint planetary nebulae.

Deep look at Sagittarius

This map locates our featured galaxies and galaxy stand-in in Sagittarius. The constellation is close to the meridian at dusk in late August. Saturn’s place is proven for August 21, 2019. Click on to enlarge and save.
Stellarium

Barnard’s Galaxy is 1.6 million light-years away and resembles the Small Magellanic Cloud in each type and composition. Edwin Hubble studied the galaxy with the 100-inch Hale reflector within the early 1920s and revealed a paper titled “N.G.C. 6822, A Distant Stellar System,” which included observations of 11 Cepheid variables. Utilizing Henrietta Leavitt’s interval–luminosity relationship, he decided the gap to NGC 6822 at 700,000 light-years, greater than double Harlow Shapley’s estimate. Hubble’s remark was an early nail within the coffin of the extra constricted universe favored by Shapley and his followers on the time.

Eyecatchers in Sagittarius

The shut pair of galaxies, NGC 6835 and NGC 6836, shine from the northwest nook of Sagittarius. The latter is a barred spiral with a construction much like the our personal Milky Approach.
Rick Johnson / CC BY-NC-ND four.zero

Transferring to the northwest nook of Sagittarius, I sought out a pair of faint NGC galaxies, NGC 6835 and NGC 6836. Though it was faint at magnitude 12.5, I pretty rapidly noticed the edge-on spiral NGC 6835. The brighter core bled into narrower arms that prolonged to the east and west. The view was a lot better at 142× and 245×. NGC 6536, situated in the identical 142× subject of view 7′ due south, glowed wanly at magnitude 12.9. It was far more diffuse object that required averted imaginative and prescient to see. I noticed a spherical haze with a faint foreground star concerned 142×. With effort I copped a delightful view of each galaxies on the identical time.

It is a pleasure to spend time in Sagittarius with all of the great, vibrant deep-sky objects the Milky Approach offers. But when you’ll want to go away the galaxy for a style of the unique, you are able to do that, too.



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