ASTR1001
Planet Zog: Background Briefing and
First Data Release
The Planet Zog
Imagine that you live on the distant planet Zog: far away in
a space-time very different from our own. Zog is very much
like the Earth: you have a technology virtually identical to
our own. All the laws of Physics, as you measure them in
the Zoggian laboratories, seem identical to the laws we
measure on Earth.
The one thing that is very different is the night sky...
The stars look similar
to Earth’s, but there is
no Milky Way.
Instead, north Zog
astronomers see
the awesome
sight of the
Greater Milkstain
With its brilliant offcentre blue spot.
Southern hemisphere
Zog astronomers see
the equally brilliant
southern blue spot.
Recent Bubble Space Telescope observations have shown
that the southern blue spot also has an off-centre milkstain
associated with it. But the Southern Milk Stain is very very
much smaller and fainter than its northern counterpart.
Celestial Coordinates.
The two blue spots are diametrically opposite on the sky
(and hence can never both be seen at the same time,
except by astronauts).
They are used as the origin of the celestial coordinate
system:
Declination: +90 for
northern blue spot,
0 for the celestial
equator.
Right Ascension: 0 to
360. Zero axis is along
the long axis of the two
milkstains.
Both milkstains
extend away from
the two blue spots
in the same
direction (though
the GMS extends
further).
The Milkstains
The Greater Milkstain (GMS) has been known for centuries
to break up into literally millions of stars when viewed with
even a pair of binoculars. There appear to be about ten
millions stars in total.
The Lesser Milkstain (LMS) does not break up into stars
when observed with telescopes. It does, however, have
some rather curious jet-like features emerging from it:
The Fuzzballs
In addition to stars, some curious fuzzy objects are seen
scattered, with roughly uniform number density, all around
the sky. They are similar to the jet-like features extending
from the Southern Blue Spot (SBS). They vary enormously
in brightness and size, though the larger ones tend to be
brighter. Faint fuzzballs greatly outnumber the bright ones.
Most fuzzballs are brighter and bigger than the LMS.
The Blue Spots
Both blue spots are roughly equally bright. They do not
vary in brightness. Both are about as bright as a full moon.
They are not just dots: they seem to consist of blue-white
cores, surrounded by a paler fuzz that merges into the two
Milkstains.
Recent Observations
We now present some recent observations made by
Zoggian astronomers.
Note that Zoggian astronomers use SI units, just like
earthlings.
Schnunka et al.
Schnunka et al. (from Mt Ztromlo Observatory) recently
carried out, and published, a rather interesting study of
fuzzballs. They obtained images of fuzzballs using the
Bubble Space Telescope (BST). They asked for
observations of the ten brightest and ten faintest fuzzballs.
The BST time allocation committee allocated half the time
they asked for, allowing observations of ten fuzzballs in total
(they were not convinced that the extra time would tell them
anything interesting). The brightest five were taken from the
Messier catalogue of bright fuzzballs.
The Bubble Space Telescope
They asked for observations of the ten faintest fuzzballs.
Nobody has ever found the faintest fuzzballs: the harder
you look, the more faint fuzzballs you see. Nobody has yet
found a lower limit on how faint they can get. Also, really
faint fuzzballs are very hard to observe: you need a huge
telescope and a lot of exposure time. The time allocation
committee therefore chose to give them observations of
the five faintest fuzzballs in the New Fuzzball Catalogue, a
catalogue of the thousand brightest fuzzballs in the sky.
All observations were made though a filter (the V filter) that
allows light in the wavelength range 0.45-0.55 m to pass.
Fluxes are quoted in W m-2 nm-1, ie. the rate at which
energy hits a unit area of the telescope, per unit
wavelength range the instrument is sensitive to.
Here is the picture of the brightest fuzzball: M23. Note that
it is clearly made up of stars: around 10 million of them.
Here is the picture of
the faintest fuzzball:
NFC 761. Note the lack
of detail: even with the
Bubble Space
Telescope, you cannot
pick out details.
The faintest fuzzballs
appear considerably
smaller than the near
ones. Their central
surface brightness
(Watts per square
arcsecond), however,
is roughly the same.
Fuzzball Right
Declination Total Flux from
Name
Ascension
Fuzzball
(w m-2 nm-1)
M23
310.68
-12.87
2.59x10-15
M86
153.0
-33.39
6.9x10-16
M99
187.92
+8.64
2.2x10-16
M19
43.92
+9.72
6.6x10-17
M6
112.32
+27.99
4.5x10-17
NFC531
9.36
+13.23
1.7x10-19
NFC64
236.88
-70.20
1.3x10-19
NFC39
98.28
+60.75
8.6x10-20
NFC245
166.68
-18.36
1.6x10-19
NFC761
357.84
-74.61
7.4x10-20
Flux from brightest
stars in fuzzball
(w m-2 nm-1)
2.1x10-22
7.54x10-23
2.26x10-23
4.7x10-23
2.9x10-23
No stars resolved
No stars resolved
No stars resolved
No stars resolved
No stars resolved
In all cases, the surface brightness of the fuzzballs
declines with distance from the centre of the fuzzball r as:
F e
r

 r0



1
4
The colours of the inner and outer parts of the fuzzballs
are fairly similar, though the insides do appear to be
marginally bluer in some cases.
Snag et al. (Max Zlank Institute)
These researchers recently published spectra of four
fuzzballs in the jet extending from the Southern Blue Spot.
Their observations were taken with the Kemini Telescope.
The Kemini Telescope
They obtained spectra of four fuzzballs from one of the
biggest jets, as shown below. The other fuzzballs were
much fainter and would have taken more telescope time
than was available to obtain adequate spectra.
G1
G2
G3
G4
Relative Flux
All four fuzzballs had similar spectra: spectra resembling
those of typical stars.
Observed Wavelength (nm)
The only significant differences between the spectra were
that the lines were shifted. For example, hydrogen
normally emits strongly (in the lab) at a wavelength of
486.1nm (due to electrons jumping from energy level 4 to
energy level 2), and Oxygen at 372.7 nm. Here are the
observed wavelengths of these lines:
Fuzzball
name
G1
Observed Wavelength
of the Hydrogen 4-2
line
485.64 nm
Observed
Wavelength of the
O+ line
372.33 nm
G2
484.02 nm
371.09 nm
G3
482.41 nm
369.85 nm
G4
480.78 nm
368.60 nm
Nearby
Stars
486.13 nm
372.70 nm
Hoddly et al. (Green Mountain Observatory)
These researchers recently used the Bubble Space Telescope to
measure the parallaxes of ten nearby stars. The ten brightest stars near
declination zero were chosen. Measurable parallaxes were determined
for all ten stars: it turns out that they are all at a distance of around
1017m. All ten have measured fluxes of around 10-11 W m-2 nm-1 in the V
band.
One of these ten stars is a known variable: it pulses every three hours.
The other nine are not known to be variable. The variable star has a
maximum flux of 10-11 W m-2 nm-1 .
Costello et al. (Zarvard University)
This group didn’t make any new observations. Instead, they
extracted information on the twenty brightest fuzzballs from
the archives of the IRAS (Infra Red Astronomy Satellite)
spacecraft.
The IRAS data was easy to obtain: during its 2 year mission
IRAS photographed the whole sky: they just had to extract
the relevant scans from ZASA’s (the Zog Air and Space
Administration) computer archives.
IRAS mapped the whole sky at a wavelength of 60 microns.
The IRAS images were very disappointing. None of the fuzzballs emitted any
detectable mid-IR flux. The only thing detected was the Southern Blue Spot, and even
it was quite weak in the mid-IR.
Mid-IR radiation is emitted by objects with temperatures of around 100K. This usually
means interstellar dust: stars are too hot to emit much mid-IR flux. So: whatever the
fuzzballs are, they do not contain much interstellar dust.
Dust normally forms wherever stars are dying: the winds from old stars (planetary
nebulae) contain heavy elements synthesised by nuclear fusion in their cores, and as
the winds cool, these heavy elements condense out as tiny grains of graphite and
silicates.
As these dust grains float around in space, starlight heats them up to around 100K, and
they emit copious mid-IR radiation. But not in the fuzzballs.
Dust can be destroyed either by shockwaves, or by prolonged exposure to high
temperature gas (one million degrees or more).
Lightnarg & Woolley (Zalifornia Institute of
Technology)
This group have recently gone observing, with the aim of getting
spectra of as many fuzzballs as possible.
The spectra were taken with the Mt Ztromlo 2.3m Advanced
Technology Telescope. Unfortunately, this observatory is
famous for cloudy weather: they only managed to get spectra
of five fuzzballs and the Southern Milkstain through gaps in the
clouds.
Relative Flux
All five fuzzballs and the Southern Milk Stain have spectra
that look like this. The SMS was far fainter than the
fuzzballs.
Observed Wavelength (nm)
Fuzzball
Name
M23
M86
M48
M81
M22
LMS
Nearby
Stars
Right
Declination Wavelength of Hydrogen
Ascension
Level 4-2 line
310.68
-12.87
486.19
153.0
-33.39
486.22
206.28
-89.55
486.02
244.8
-27.00
487.29
246.6
-4.36
488.69
354.96
-90
484.51
486.13
They measured the wavelength of the H-beta line of
Hydrogen: a spectral line with a laboratory wavelength of
486.13 nm. In all their spectra, this line had moved in
wavelength one way or another by a small amount.
Hooligan & Thug, Zliverpool Tech
This group have spend the last year searching for supernovae with
the 1m telescope at Siding Zpring Observatory. They slaved away at
the telescope, taking thousands of pictures of various fuzzballs,
looking for something that changed.
They found four supernovae. One was in the well known bright
fuzzball M86. Three were found in fainter fuzzballs: in M12,
NFC64 and, remarkably, in a fuzzball in one of the jets protruding
from the Northern Blue Spot: B3.
The 1m
Here are the before- and after images
of the supernova in NFC64. The top
image was taken while the supernova
was at maximum brightness - the
bottom one before it had exploded.
All the supernovae had very similar
spectra, and they all showed the same
pattern of brightening and fading.
Here is a table of the peak brightness reached by the
various supernovae.
Fuzzball in which
Average Peak V-band Flux
supernova was found (Wm-2nm-1)
M86
4.0x10-11
M12
4.2x10-14
NFC64
9.2x10-15
B3
1.1x10-15
Chuck & Bride, Louiziana College of TAFE
These eminent researchers obtained spectra of the Greater
Milkstain, and of both blue spots, using the William Herzhal
Telescope in the Izlas Canarias.
The William Herzhel Telescope
Relative Flux
The GMS is made up of many individual stars. To avoid being biassed
by some particular star, the spectrograph slit was scanned across the
GMS. Here is the integrated Spectrum. It has no red- or blue-shift.
Observed Wavelength (nm)
Energy per unit Wavelength
The spectra of both blue spots were identical. There are no
bumps or wiggles in the spectrum to measure a redshift
from.
300
Wavelength (nm)
1000