NGC 3603

NGC 3603 is a nebula situated in the Carina–Sagittarius Arm of the Milky Way around 20,000 light-years away from the Solar System. It is a massive H II region containing a very compact open cluster HD 97950.

Observations

NGC 3603 was observed by John Herschel on 14 March 1834 during his visit to South Africa, who remarked that it was "a very remarkable object...perhaps a globular cluster". Herschel catalogued it as nebula 3334 in his Results of Astronomical Observations made at the Cape of Good Hope, published in 1847. In 1864 the Royal Society published his General Catalogue of Nebulae and Clusters, where he listed it as number 2354. It was subsequently incorporated into the New General Catalogue as by J. L. E. Dreyer as NGC 3603.
The central cluster was catalogued as the star HD 97950, but has long been recognised as nebulous or multiple. It was also noted for having an unusual emission spectrum and the spectral type was given as Oe in the Henry Draper Catalogue. This was later refined to WN5 + O as the emission was recognised as characteristic of a Wolf–Rayet star. Eventually, the cluster would be resolved and found to contain three of the most massive and most luminous stars known, as well as a number of luminous O class stars and many fainter stars.

Features

NGC 3603 is the most massive visible cloud of glowing gas and plasma, known as a H II region, in the Milky Way. The central star cluster is the densest concentration of very massive stars known in the galaxy. Strong ultraviolet radiation and stellar winds have cleared the gas and dust, giving an unobscured view of the cluster.
Three prominent Wolf–Rayet stars have been detected within the cluster, all originally unresolved and known as the single star HD 97950. The brightest of the three, HD 97950A1 is actually a pair of Wolf–Rayet stars that orbit around each other once every 3.77 days. The primary is an estimated mass, while its companion is. The star designated HD 97950B is a single star more massive and more luminous than either of the individual members of HD 97950A1. It is 2,880,000 times as luminous as the sun and 132 times as massive.
NGC 3603 is visible in the telescope as a small rather insignificant nebulosity with a yellowish tinge due to the effects of interstellar absorption. In the mid-1960s, optical studies combined with radio astronomical observations showed it to be an extremely strong thermal radio source. Later observations of other galaxies introduced the concept of starburst regions, in some cases whole galaxies, of extremely rapid star formation. NGC 3603 is now considered to be such a region, and it has been compared by some authors to the larger cluster 30 Doradus, in the Large Magellanic Cloud.
Sher 25, a B class supergiant, has long been thought to be a member of NGC 3603, but turns out to be a foreground star. is surrounded by ejected material in an hourglass shape similar to that found for the supernova 1987A, and this has aroused intense interest in the future evolution of stars such as Sher 25.
Two of the most luminous young stars known are found within NGC 3603, but outside the central cluster. WR 42e and NGC 3603 MTT 58 both have a spectral type of O2If*/WN6 indicating an extremely massive young star. WR 42e is a possible runaway from a three-body encounter, while MTT 58 appears to still be embedded within its parental cocoon and is in a possible binary with an O3If star.

MDS number	MTT number	Other names	Spectral type	m_V	M_V	Temperature	Luminosity	Reference
30		WR 43a	WN6h/WN6h	11.18	−7.8	42,000/40,000	2,455,000/1,514,000
31		HSW 4	O3V	12.53	−6.9	46,500	1,500,000
26		HSW 5	O3III	13.09	−6.4	46,500	863,000
23		WR 43b	WN6h	11.33	−7.9	42,000	2,884,000
18		WR 43c	WN6h	11.89	−7.3	44,000	2,239,000
49			O4V	12.64	−6.3	44,000
50			O5V	12.74	−6.2	41,000
52			O4V	13.68	−5.2	44,000
19		MMM 104	O5.5III	12.83	−6.1	41,000	1,038,000
39	6		O5V	11.86	−6.1	41,000
61	10		O5V	12.74	−6	41,000
	58	WR 43-2	O2If*/WN6	14.76	−5.7		855,000
		WR 42e	O2If*/WN6	14.53	−6.3		1,300,000
29			O4V	13.68	−5.2	44,000
27			O4V	13.07	−5.8	44,000
25			O4V	13.01	−5.9	44,000
40			O3V	13.33	−5.7	46,500	718,000
33			O5V+OB?	13.69	−5.8
41			O4V	14.24	−5.1	44,000	217,000
42			O3III	12.99	−6.1	46,500	946,000
37			O6.5V+?	14.16	−5
38			O3V	13.21	−5.9	46,500	497,000
16			O3V	13.53	−5.4	46,500	655,000
43		MMM 111	O4V	13.87	−5	44,000
14			O4V	13.88	−5	44,000
59			O4V	13.65	−5.3	44,000
60			O4V	13.6	−5.3	44,000
62			O4V	13.09	−5.6	44,000
58		MMM 101	O6.5V)	14.02	−5.1	37,000	238,000
51	23	Sher 56	O4V	13.33	−5.6	44,000
9		MMM 108	O5.5V	13.71	−5.5	39,500	377,000
7	26	Sher 64	O4V	13.58	−5.4	44,000	863,000
22	17	Sher 57	O5III	13.23	−5.8	41,000	787,000
1	12	Sher 23	OC9.7Ia	12.7	−6.3	30,250	413,000
2	18	Sher 22	O3III	13.21	−5.6	46,500	863,000
48	14	Sher 18	O3.5If	12.65	−6.4	39,500	1,644,000
24	11	Sher 47	O4V	12.72	−6.2	44,000	1,644,000
20			O4V	13.98		44,000
76	39	Sher 54	O6V	14.57	−4.6	38,300	150,000
17		MMM 116	O4V	14.1		44,000
36			O6V	14.52	−4.2	38,300	114,000
45			O8V-III	14.14	−4.7	33,700	114,000
4	41	Sher 49	O7.5V	14.67	−4.6	34,800	114,000
57			O4V	13.98		44,000
10		MMM 117	O6V	14.17	−5.1	38,300	238,000
3	32	Sher 24	O6V	14.27	−5	38,300	217,000
	51	Sher 27	O7.5V	15.04	−4	34,800	65,000
	15	Sher 63	O3.5III	13.41	−5.6	45,000	597,000
63	40	Sher 53	O8.5V	14.47	−4.8	32,700	125,000
73		MMM 102	O8.5V	15.32	−3.9	32,700	50,000
	47	Sher 21	O6V)	14.75	−4.6	38,300	150,000
	25	Sher 19	O3V	12.61	−6.2	46,500	497,000
		MMM 103	O3V)	13.09	−5.7	46,500	718,000
		MMM 109	O7V	13.85	−4.9	36,000	180,000