SN 1572. Tycho's Supernova

 

A star map of the constellation Cassiopeia showing the position of the supernova of 1572, the topmost star, labelled I, from Tycho Brahe's De nova stella. Credit: Tycho Brahe/Wikimedia Commons

Supernova SN 1572, also known as Tycho's Supernova or Tycho's Nova, was a supernova of Type Ia in the constellation Cassiopeia, one of eight supernovae visible to the naked eye in historical records. It appeared in early November 1572 and was independently discovered by many individuals. Its discovery marked a milestone in the history of science, challenging the Aristotelian dogma of the immutability of the realm of stars. 

 
   SN 1572 was well observed in Europe, as well as in the Far–East, for 16 months before fading from sight. The supernova was not yet noticeable on November 2, and its first observation was done on November 6 by German astronomer Wolfgang Schüler of Wittenberg. On November 11 it seems to have achieved a magnitude between those of Jupiter and Venus. On November 16 and 17, it reached its peak brightness at about magnitude −4.0, close to the magnitude of Venus. Later on, in January 7, 1573, it was already fainter than Jupiter. The supernova remained visible to the naked eye into early 1574, gradually fading until it disappeared from view.

 

   Tycho Brahe (1546–1601) first noticed a new, bright star in the constellation of Cassiopeia on November 11, 1572. He wrote (from Burnham’s Celestial Handbook):

"On the eleventh day of November in the evening after sunset ... I was contemplating the stars in a clear sky. … I noticed that a new and unusual star, surpassing the others in brilliancy, was shining almost directly above my head; and since I had, from boyhood, known all the stars of the heavens perfectly, it was quite evident to me that there had never been any star in that place in the sky, even the smallest, to say nothing of a star so conspicuous and bright as this. I was so astonished at this sight that I was not ashamed to doubt the trustworthiness of my own eyes. But when I observed that others, on having the place pointed out to them, could see that there was really a star there, I had no further doubts. A miracle indeed, one that has never been previously seen before our time, in any age since the beginning of the world."

   and (from Tycho Brahe, 1602, Astronomiae Instauratae Progymnasmata):

“I suddenly and unexpectedly beheld near the zenith an unaccustomed star with with a bright radiant light. Astounded, as though thunderstruck by this astonishing sight, I stood still and for some time gazed with my eyes fixed intently upon this star. It was near the stars which have been assigned since antiquity to the asterism of Cassiopeia. I was convinced that no star like this had ever before shone forth in this location....

At the beginning, its apparent magnitude exceeded all of the fixed stars, including those of the first magnitude, and even the Dog Star itself and the brightest star in Lyra. Indeed, the new star appeared brighter than Jupiter... when closest to the Earth. It rivaled the brilliant aspect of Venus when nearest to the Earth. During November the new star was so bright that, when the air was clear, many people with sharp vision were able to see it in the daytime, even at midday.”

   Tycho was not the first to see the new star, but by observing it with an astronomical radius and a half-sextant, he determined that the star exhibited no diurnal parallax whatsoever. Tycho concluded that the star must be farther away than the Moon and in fact it lies in the sphere of the fixed stars. This contradiction to the Aristotelian concept, that a change on the sky can only occur in the sub-lunar regime, ultimately led to abandoning the immutability of the heavens. Tycho published his findings in a book entitled De nova stella (1573).  

The red circle visible in the upper left part of this Wide-field Infrared Survey Explorer (WISE) infrared image is the remnant of SN 1572. The image spans an area of 1.6 x 1.6 degrees.
Color code: blue and cyan represent infrared light at wavelengths of 3.4 and 4.6 microns, which is dominated by light from stars. Green and red represent light at 12 and 22 microns, which is mostly light from warm dust. Credit: NASA/JPL-Caltech/WISE Team

   The SN 1572 supernova remnant was first discovered in 1952 at radio waves. It is often known as 3C 10, a radio-source designation, although increasingly as Tycho's supernova remnant. The distance to the remnant has been estimated to between 2.5 and 3 kpc (approximately 8,000 and 9,800 light-years). Tycho's SNR has a roughly spherical morphology and spreads over an angular diameter of about 8 arcminutes. Its physical size corresponds to radius of the order of a few parsecs. Its measured expansion rate is about 0.11–0.12 per cent/year in radio and X-ray. The average forward shock speed is between 4,000 and 5,000 km/s, dropping to lower speed when encountering local interstellar clouds.

   Recent observations in 2008 have revealed, by detecting its optical spectrum near maximum brightness from the scattered-light echo, that SN 1572 belongs to the class of Type Ia supernova. A red subgiant has been suggested to be the possible surviving companion of the supernova in a close binary system. However, the evolutionary path of the progenitor is still not understood, and this association has been questioned.

   Type Ia supernovae are thermonuclear explosions of white dwarf stars in close binary systems. This violent explosion occurs when a white dwarf star pulls material off its companion star until it reaches a mass limit, or when two white dwarfs merge. The obliteration of the white dwarf sends debris hurtling into space at tremendous speeds. Type Ia supernovae play an important role as cosmological distance indicators and have led to the discovery of the accelerated expansion of the Universe. 

This image of Tycho's supernova remnant in X-rays from the Chandra X-ray Observatory. Low and medium energy X-rays in red and green show expanding debris from the supernova explosion. High energy X-rays in blue reveal the blast wave, a shell of extremely energetic electrons. Also shown in the lower left region of the remnant is a blue arc of X-ray emission. Several lines of evidence support the conclusion that this arc is due to a shock wave created when a white dwarf exploded and blew material off the surface of a nearby companion star. Image is 10 arcmin across (about 38 light years).
Color code: Energy: Red 1.6-2.0 keV, Green 2.2-2.6 keV, Blue 4-6 keV
Credit: NASA/CXC/Chinese Academy of Sciences/F. Lu et al

 

In this composite image, data from NASA’S Imaging X-ray Polarimetry Explorer (IXPE) (dark purple and white) have been combined with those from the Chandra X-ray Observatory (red and blue), which were overlaid with the stars in the field of view seen by the Digitized Sky Survey. Image is about 16 arcmin (60 light-years) across.
Color code: Chandra X-ray: red & blue; IXPE X-ray: purple & white; Optical: white, red, blue
Credit: X-ray (IXPE: NASA/ASI/MSFC/INAF/R. Ferrazzoli, et al.), (Chandra: NASA/CXC/RIKEN & GSFC/T. Sato et al.) Optical: DSS
Image processing: NASA/CXC/SAO/K. Arcand, L. Frattare & N. Wolk

© 2025, Andrew Mirecki