When the star that created this supernova remnant
exploded in 1572, it was so bright that it was visible during the day.
And though he wasn't the first or only person to observe this stellar
spectacle, the Danish astronomer Tycho Brahe wrote a book about his
extensive observations of the event, gaining the honor of it being named
after him.
In modern times, astronomers have observed the debris field from this
explosion - what is now known as Tycho's supernova remnant - using data
from NASA's Chandra X-ray Observatory,
the NSF's Karl G.
Jansky Very Large Array (VLA) and many other
telescopes. Today, they know that the Tycho remnant was created by the
explosion of a white dwarf star, making it part of the so-called Type Ia class of supernovas used to track the expansion of the Universe.
Since much of the material being flung out from the shattered star
has been heated by shock waves - similar to sonic booms from supersonic
planes - passing through it, the remnant glows strongly in X-ray light.
Astronomers have now used Chandra observations from 2000 through 2015
to create the longest movie of the Tycho remnant's X-ray evolution over
time, using five different images. This shows the expansion from the
explosion is still continuing about 450 years later, as seen from
Earth's vantage point roughly 10,000 light years away.
By combining the X-ray data with some 30 years of observations in radio waves with the VLA,
astronomers have also produced a movie, using three different images.
Astronomers have used these X-ray and radio data to learn new things
about this supernova and its remnant.
The researchers measured the speed of the blast wave at many
different locations around the remnant. The large size of the remnant
enables this motion to be measured with relatively high precision.
Although the remnant is approximately circular, there are clear
differences in the speed of the blast wave in different regions. The
speed in the right and lower right directions is about twice as large as
that in the left and the upper left directions. This difference was
also seen in earlier observations.
This range in speed of the blast wave's outward motion is caused by
differences in the density of gas surrounding the supernova remnant.
This causes an offset in position of the explosion site from the
geometric center, determined by locating the center of the circular
remnant. The astronomers found that the size of the offset is about 10%
of the remnant's current radius, towards the upper left of the geometric
center. The team also found that the maximum speed of the blast wave is
about 12 million miles per hour.
Offsets such as this between the explosion center and the geometric
center could exist in other supernova remnants. Understanding the
location of the explosion center for Type Ia supernovas is important
because it narrows the search region for a surviving companion star. Any
surviving companion star would help identify the trigger mechanism for
the supernova, showing that the white dwarf pulled material from the
companion star until it reached a critical mass and exploded. The lack
of a companion star would favor the other main trigger mechanism, where
two white dwarfs merge causing the critical mass to be exceeded, leaving
no star behind.
The significant offset from the center of the explosion to the
remnant's geometric center is a relatively recent phenomenon. For the
first few hundred years of the remnant, the explosion's shock was so
powerful that the density of gas it was running into did not affect its
motion. The density discrepancy from the left side to the right has
increased as the shock moved outwards, causing the offset in position
between the explosion center and the geometric center to grow with time.
So, if future X-ray astronomers, say 1,000 years from now, do the same
observation, they should find a much larger offset.
A paper describing these results has been accepted for publication in The Astrophysical Journal Letters and is available online.
The authors are Brian Williams (NASA's Goddard Space Flight Center),
Laura Chomiuk (Michigan State University), John Hewitt (University of
North Florida), John Blondin (North Carolina State University),
Kazimierz Borkowski (NCSU), Parviz Ghavamian (Towson University), Robert
Petre (GSFC), and Stephen Reynolds (NCSU).
NASA's Marshall Space Flight Center in Huntsville, Alabama, manages
the Chandra program for NASA's Science Mission Directorate in
Washington. The Smithsonian Astrophysical Observatory in Cambridge,
Massachusetts, controls Chandra's science and flight operations.
Fast Facts for Tycho's Supernova Remnant:
Scale: Image is 15 arcmin across (about 44 light years)
Category: Supernovas & Supernova Remnants
Observation Date: 13 pointings between 2000 and 2015
Observation Time: 325 hours 17 min (13 days 13 hours 17 min)
Obs. ID: 115, 3837, 7639, 8551, 10093-10097; 10902-10904; 10906, 15998
Instrument: ACIS
Also Known As: G120.1+01.4, SN 1572
References: Williams, B. et al, 2016, ApJL (accepted); arXiv:1604.01779
Color Code: X-ray (Red 0.95-1.26 keV, Green 1.63-2.26 keV, Blue 4.1-6.1 keV), Optical (Red, Green, Blue)
Distance Estimate: About 13,000 light years
