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 off-

centre 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 MilkstainsThe 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 FuzzballsIn 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 mm 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

Name

Right

Ascension

Declination Total Flux from

Fuzzball

(w m-2 nm-1)

Flux from brightest

stars in fuzzball

(w m-2 nm-1)

M23 310.68 -12.87 2.59x10-15 2.1x10-22

M86 153.0 -33.39 6.9x10-16 7.54x10-23

M99 187.92 +8.64 2.2x10-16 2.26x10-23

M19 43.92 +9.72 6.6x10-17 4.7x10-23

M6 112.32 +27.99 4.5x10-17 2.9x10-23

NFC531 9.36 +13.23 1.7x10-19 No stars resolved

NFC64 236.88 -70.20 1.3x10-19 No stars resolved

NFC39 98.28 +60.75 8.6x10-20 No stars resolved

NFC245 166.68 -18.36 1.6x10-19 No stars resolved

NFC761 357.84 -74.61 7.4x10-20 No stars resolved

In all cases, the surface brightness of the fuzzballs

declines with distance from the centre of the fuzzball r as:

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.

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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

G2G3

G4

All four fuzzballs had similar spectra: spectra resembling

those of typical stars.

Observed Wavelength (nm)

Rela

tive F

lux

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

Observed Wavelength

of the Hydrogen 4-2

line

Observed

Wavelength of the

O+ line

G1 485.64 nm 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.

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)

Rela

tive F

lux

Fuzzball

Name

Right

Ascension

Declination Wavelength of Hydrogen

Level 4-2 line

M23 310.68 -12.87 486.19

M86 153.0 -33.39 486.22

M48 206.28 -89.55 486.02

M81 244.8 -27.00 487.29

M22 246.6 -4.36 488.69

LMS 354.96 -90 484.51

Nearby

Stars

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 whichsupernova was found

Average Peak V-band Flux(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

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)

Rela

tive F

lux

The spectra of both blue spots were identical. There are no

bumps or wiggles in the spectrum to measure a redshift

from.

Wavelength (nm)

Energ

y p

er

unit W

avele

ngth

300 1000