Herschel Detects a Massive Dust Reservoir in Supernova 1987A
M. Matsuura, et al.
Science 333, 1258 (2011);
DOI: 10.1126/science.1205983

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Herschel Detects a Massive DustReservoir in Supernova 1987A
M. Matsuura,1,2* E. Dwek,3 M. Meixner,4 M. Otsuka,4 B. Babler,5 M. J. Barlow,1 J. Roman-Duval,4
C. Engelbracht,6 K. Sandstrom,7 M. Lakićević,8,9 J. Th. van Loon,8 G. Sonneborn,3 G. C. Clayton,10
K. S. Long,4 P. Lundqvist,11 T. Nozawa,12 K. D. Gordon,4 S. Hony,13 P. Panuzzo,13 K. Okumura,13
K. A. Misselt,6 E. Montiel,6 M. Sauvage13
We report far-infrared and submillimeter observations of supernova 1987A, the star whose explosion
was observed on 23 February 1987 in the Large Magellanic Cloud, a galaxy located 160,000 lightyears away. The observations reveal the presence of a population of cold dust grains radiating with atemperature of about 17 to 23 kelvin at a rate of about 220 times the luminosity of the Sun. The intensity
and spectral energy distribution of the emission suggest a dust mass of about 0.4 to 0.7 times the mass of
the Sun. The radiation must originate from the supernova ejecta and requires the efficient precipitation of
all refractory material into dust. Our observations imply that supernovae can produce the large dust
masses detected in young galaxies at very high redshifts.
upernovae produce most of the heavy
elements found in the universe and disperse them into their surrounding galactic
environment. They chemically enrich the material from which new generations of stars andplanets are formed. The explosion of supernova(SN) 1987A was first observed from Earth on
23 February 1987 in the Large Magellanic Cloud(LMC), only 50 kpc away. Because of its proximity, it has been possible to witness its evolution
from explosion to remnant. SN 1987A has thus
become one of the most extensively studied extragalactic objects, with ground, airborne, andspace observatories covering a wide range of theelectromagnetic spectrum. Here, we report farinfrared and submillimeter (submm) observations of SN 1987A.
Previous observations of Supernova 1987A.
The detection of neutrinos from SN 1987A confirmed that the event marked the explosive deathS

1
Astrophysics Group, Department of Physics and Astronomy,
University College London, Gower Street, London WC1E 6BT,
UK. 2Mullard Space Science Laboratory, University College
London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK.
3
Observational Cosmology Laboratory, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA. 4Space
Telescope Science Institute, 3700 San Martin Drive, Baltimore,
MD 21218, USA. 5Department of Astronomy, 475 North Charter
St., University of Wisconsin, Madison, WI 53706, USA. 6Steward
Observatory, University of Arizona, Tucson, AZ 85721, USA.
7
Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117
Heidelberg, Germany. 8Astrophysics Group, Lennard-Jones Laboratories, Keele University, ST5 5BG, UK. 9European Southern
Observatory, Karl Schwarschild Straße 2, D-85748 Garching bei
München, Germany. 10Louisiana State University, Departmentof Physics and Astronomy, 233-A Nicholson Hall, Tower Drive,
Baton Rouge, LA 70803–4001, USA. 11Department of Astronomy, The Oskar Klein Centre, AlbaNova University Center,
Stockholm University, SE-106 91 Stockholm, Sweden. 12Institute for the Physics and Mathematics of the Universe, Universityof Tokyo, Kashiwa, Chiba 277-8583, Japan. 13Commissariat àl’Energie Atomique et aux Energies Alternatives, Laboratoire
Astrophysique, Instrumentation et Modélisation, Irfu/SAp, Ormedes Merisiers, F-91191 Gif-sur-Yvette, France.

*To whom correspondence should be addressed. E-mail:mikako@star.ucl.ac.uk

1258

of a massive star (1, 2). The intensity and evolution of its ultraviolet (UV) and optical light
curves showed that the SN’s luminosity was
powered by the radioactive decays of 56Ni and56
Co, yielding 0.06 times the mass of the Sun(M⊙) of 56Fe (3). The g-rays and x-rays fromradioactive nuclei emerged only 4 months after
the explosion (4, 5), suggesting that the ejecta
were clumpy (6). The large width of near- andmid-infrared spectral lines of heavy elements (7)indicated that the newly synthesized material
from the stellar core had undergone substantial
mixing into the outer ejecta of the stellar explosion (6). SN 1987A was classified as a type II
event on the basis of the detection of hydrogen in
its optical spectrum (8).
Examination of plates of the region obtained
before the SN explosion allowed the detection of
its progenitor, a blue supergiant (Sk-69 202) thatwas believed to have had an initial mass of 18 to
20 M⊙ (8). The progenitor underwent extensive
mass loss during its post main-sequence evolution (8). The detection and evolution of UV lines
from highly ionized gas revealed previously ejectedmaterial that was flash ionized by the x-ray andUV radiation released when the outwardly expanding shock generated by the collapse of thestellar core broke out through the surface of theprogenitor star (9). The presence of progenitor
material was later confirmed by Hubble Space
Telescope observations, which revealed a thin elliptical ring (1.6′′ by 1.2′′) (10) containing manyknots within it (11). The equatorial ring is part ofa system of three rings forming an hourglass-like
configuration centered on the explosion. The massof the ring is estimated to be > ~6 × 10–2 M⊙ (12).
Mid-infrared spectral and photometric observations of SN 1987A obtained with the Kuiper
Airborne Observatory (13) revealed the presenceof newly formed dust in the SN, providing direct
evidence for the formation of grains in the cooling ejecta of a supernova. The dust condensation
process started around day 450 to 600 after the

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explosion was observed (14, 15); it is thoughtthat dust had condensed in the clumps within theejecta (16). The dust mass was estimated to be atleast ~10−4 M⊙ (17).
Several years after the explosion was observed, SN 1987A had evolved from a SN remnant radiating as a result of radioactive decays,
mainly 56Co and 44Ti (3), into a remnant where
the interaction of the SN blast wave with thecircumstellar medium is causing the ring tobrighten up. This interaction, dominated by thecollision between the blast wave and the equatorial ring, manifested through the appearance of
UV-optical hot spots strung like beads around thering (18). Similar ring structures were also observed at x-ray wavelengths and in the midinfrared (19).
Subsequent spectral observations with the Spitzer Space Telescope on days 6200 to 8000 (20)revealed strong infrared (6 to 30 mm) emission
arising from about 10−6 M⊙ of silicate dust in the
inner ring that had been collisionally heated to atemperature of 180 K by the shocked x-ray emitting gas. The dust in the ring was ejected during
the pre-SN evolution of the progenitor star.
Observations and results. Using the HerschelSpace Observatory’s (21) imaging instruments,
the Photodetector Array Camera and Spectrometer (PACS) (22) and the Spectral and Photometric Imaging Receiver (SPIRE) (23), we observed
SN 1987A as part of the Herschel Inventory of
the Agents of Galaxy Evolution in the Magellanic Clouds open time key program (HERITAGE)(24). The observing survey covered five bands,
PACS 100- and 160-mm and SPIRE 250-, 350-,
and 500-mm, with angular resolutions of 6.69′′ by
6.89′′, 10.65′′ by 12.13′′, 18.2′′, 24.9′′, and 36.3′′,
respectively. SN 1987Awas observed on 30 April
and 5 August 2010 (days 8467 and 8564 after
the explosion was observed).
The PACS and SPIRE images of the combined
two epochs (Fig. 1) (25) reveal SN 1987A as a faintbut detectable point source coincident with thevery-long-baseline interferometry–measured coordinates of SN 1987A: right ascension, 5h 35m
27.990s; declination, −69d 16′ 11.110′′ (J2000)(26). Spatial comparison of these images withprevious Spitzer detections with the multiband
imaging photometer (MIPS) at 24 mm and theinfrared array camera (IRAC) at 8 mm (20) confirms the location of SN 1987A with respect tonearby interstellar features. In the PACS 100- and
160-mm images, SN 1987A is clearly detected asa point source that is well separated from the nearby interstellar medium (ISM) dust. In the SPIRE
bands, the 250-mm image shows SN 1987A as apoint source, but the SN begins to merge with the
nearby ISM dust emission at 350 mm and blends
completely at 500 mm, owing to the increasing
beam size at longer wavelengths. The Hubble andSpitzer Space Telescopes and Herschel Space Observatory images (Fig. 1, A and C to H) show thatSN 1987A is located in a region with relatively
low amounts of ISM gas and dust.

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RESEARCH ARTICLESWe obtained photometry from the processed
Herschel images (Table 1) (27), assuming thatSN 1987A is unresolved; the fluxes are plotted inFig. 2A. There are two peaks in the spectral energy distribution (SED), one near 20 mm and theother at 150 to 200 mm (Fig. 2A). The total luminosity from 100 to 500 mm is ~220 times the luminosity of the Sun (L⊙). The mid-infrared (5 to40 mm) luminosity is 1200 L⊙ (epoch of 7983
days) (20), and the x-ray luminosity is ~500 L⊙(8012 days) (28). Thus, the far-infrared/submm

emission that we detected is an important component of this SN’s SED.
The origin of the far-infrared/submm emission. The smooth blackbody-like shape of the
far-infrared/submm SED (Fig. 2A) suggests continuous emission from dust. However, synchrotron emission and line emission from the samegas that produces the UV, optical, and nearinfrared lines are also possible.
Line emission can arise from the supernova
ejecta and the circumstellar rings. The rings were

Fig. 1. (A to H) The Herschel images of SN 1987A,
together with the Spitzer infrared (20) and the Hubble
optical (56, 57) images. North is top, and east is left. The two horizontal white lines indicate the position of
SN 1987A measured from radio observations. (I) Background-subtracted 350-mm image, where the background is estimated from the 250-mm residual image after the subtraction of the PSF at the position of SN
1987A. The PSFs show the resolution of the Herschel instruments. (B) shows an enlarged HST optical image,indicating the morphology of the SN remnant. [Source: (A) Hubble Heritage Team (Association of
Universities for Research in Astronomy (AURA)/Space Telescope Science Institute (STScI)/NASA); (B) NASA,
ESA, P. Challis, and R. Kirshner (Harvard-Smithsonian Center for Astrophysics)]
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first flash-ionized by the supernova and havesince recombined and cooled (12). To estimate
the contribution from ionized lines from the innerring, we extended the photoionization code of(12) to include far-infrared/submm lines. The expected line intensities of the strongest ionizedlines are 0.5 × 10−15, 1.2 × 10−15, 0.1 × 10−15, and
0.2 × 10–15 erg s–1 cm–2 for the 88-mm ([OIII]),
122-mm ([NII]), 158-mm ([CII]), and 205-mm ([NII])
lines, respectively. These line fluxes are equivalent to a 0.2% contribution to the total Herschelin-band fluxes; hence, photoionized lines make anegligible contribution to the far-infrared/submm
fluxes. Another possible contribution to the line
emission may come from the radiatively coolinggas shocked by the ejecta/ring interaction (11).
However, it is unlikely that this contribution could
be orders of magnitude higher than those fromphotoionized gas because the forbidden lines
are collisionally de-excited in the high-density
shocked gas.
Continuum synchrotron radiation can also
contribute to the emission in the Herschel bands.
The synchrotron radiation has been measured atradio frequencies up to day 8014 after the explosion (26, 29) (Fig. 2A); we extrapolated thefluxes to far-infrared wavelengths using a powerlaw. The predicted Herschel flux densities fromsynchrotron radiation are two orders of magnitude lower than those we measured (Fig. 2A),
implying that the emission observed by Herschel
is mostly due to the continuum emission from dust.
Dust mass. Using the flux densities and theiruncertainties, we calculated the dust temperatureand mass needed to account for the observations(Table 2 and Fig. 2B) (30).
We explored four possible origins for the
dust: progenitor dust, ambient ISM dust swept up
by SN shocks, a light echo from ISM dust, andSN ejecta dust.
It is thought that the progenitor of SN 1987A
ejected 8 M⊙ of gas during its red supergiant(RS) phase before the SN explosion (3). The dust
ejected this way is expected to be composed
mostly of silicates because RSs produce oxygenrich dust. Adopting a gas-to-dust mass ratio of
300 (31) implies a silicate dust mass from the RSof 0.03 M⊙. The silicate dust mass required to fit
the observed emission is much higher (>2 M⊙)(Table 2), equivalent to >600 M⊙ of gas. A

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RESEARCH ARTICLESTable 1. The measured PACS and SPIRE flux densities of SN 1987A. We added in quadrature theuncertainties from the source extraction and theabsolute errors in the flux calibration, which are
estimated to be 10% for the PACS bands and 7%
for the SPIRE bands (47, 48). *, 3-SD upper limit.
Band

Flux (mJy)

PACS 100 mm
PACS 160 mm
SPIRE 250 mm
SPIRE 350 mm
SPIRE 500 mm

70.5 T 8.5
125.3 T 16.1
131.7 T 12.1
49.3 T 6.5<57.3*

2 SEPTEMBER 20111259

similar evaluation rules out the possibility that
dust could have been formed during another evolutionary phase of the progenitor, for example, aluminous blue variable. It is therefore unlikelythat the observed far-infrared/submm emission
could have originated from dust formed by the
SN progenitor.
As it expands, the SN sweeps up dust fromthe ambient ISM. The SN shock speed is up to6000 km s–1 (32), and the distance already traveled by the shocks is up to 30,000 astronomical
units (0.6 arcsec). We assumed a gas density of
1 hydrogen atom per cm3 in the LMC ISM andadopted a gas-to-dust mass ratio of 300. Within
this volume, only a small mass of ISM dust (3 ×
10−6 M⊙) will have been swept up. This estimate

is consistent with Herschel measurements of the
ISM dust emission of <10–4 M⊙, based on thesky background level in the 160-mm band (70.4 T
9.6 MJy sr–1) measured for a 1.3 by 0.4 arcsec2
region centered at the position of SN, after removal of a point-spread function (PSF). Our measured dust emission requires a much higher dust
mass, hence favoring emission from SN dust
rather than from swept-up ISM dust.
The original SN energy pulse could potentially have been absorbed and re-emitted byinterstellar dust grains to produce infrared echoes.
To account for the Herschel fluxes, an infraredecho would have to originate from a dust cloud
located at about 11 light years directly behind
the SN, which is improbable. Moreover, thisFig. 2. (A) The infrared spectral energy distribution of SN 1987A. Herschel detected SN 1987A from 100
to 350 mm. An upper limit is given at 500 mm. The other observational data were collected from theliterature: 5.8- to 24-mm photometric data and 5- to 30-mm spectra (20), which measures the warm dust
emission; and the radio continuum (26, 29), which traces the synchrotron emission. (B) Model fits to the
far-infrared/submm dust emission using different single dust species. Parameters are given in Table 2.
(C and D) The sum of the contributions from each dust species to the far-infrared/submm spectrum of SN
1987A. The flux at each wavelength is that derived from fitting the observed spectrum with each dust
species alone (Table 2), scaled by the fraction of its mass available in the ejecta from abundance considerations (Table 4). The model 1 and model 2 abundances in Table 4 correspond to (C) and (D),respectively. The hatched areas represent the range of possible fluxes from each species, with the lower
and upper boundaries corresponding, respectively, to the scaling of the minimum and maximum and dust
masses (uncertainties in Table 2) required to produce the observed spectrum.
Table 2. Dust temperatures (Td) and corresponding dust masses (Md) derived by fitting the whole of the
far-infrared/submm emission with a single dust species (30). Quantities are insensitive to grain radius,
except metallic iron. The absorption efficiency of metallic iron depends on grain radius (a), and the table
represents the results for grain radii of 0.1 and 0.5 mm.

1260

Dust species

Md (M⊙)Td (K)

Amorphous carbon
Silicate
Iron (a = 0.1 mm)
Iron (a = 0.5 mm)

0.35 T 0.06
2.4 T 0.4
3.4 T 0.6
0.34 T 0.06

21.2 T 0.7
17.7 T 0.5
19.2 T 0.7
25.7 T 0.9

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dust would have been heated by the optical andUV light, which had a luminosity of LUVO =1041 erg sec–1 (17), implying a flux incident on
the dust F = LUVO/(4pR2), where R = 11 lightyears. Taking this energy input as the dust heating
rate, equilibrium with the dust cooling rate yields
the dust temperatures ranging from 40 K for silicate and 70 to 110 K for graphite, for a range ofgrain sizes from 0.01 to 0.1 mm (33). These temperatures are substantially higher than those measured by Herschel (Table 2), ruling out an echo as
an explanation for the Herschel SED.
Thus, we conclude that the emission observed
by Herschel is associated with cold dust in the SN
ejecta.
The dust that is being emitted at Herschelwavelengths could be heated by one or more of
the following mechanisms: (i) by the x-ray emission arising from the interaction of the blast wave
with the equatorial ring, which has a luminosityof about 500 L⊙ (20, 28); (ii) by the energy
released from the long-lived radioactive 44 Ti
isotope present in the ejecta; our measured farinfrared/submm luminosity of 220 L⊙ is about
half of the predicted 44Ti luminosity at this epoch(~ 400 L⊙) (34); or (iii) by the ambient diffuse
interstellar radiation field, given that the temperature of the far-infrared/submm emitting dust isvery similar to that of ISM dust.
The origin of the cold dust in the ejecta. The
masses predicted for the major refractory elements (Table 3) in the ejecta of SN 1987A (3, 35)
restrict the maximum mass of dust that could
have formed in the ejecta if all these elements
precipitated from the gas phase (Table 4). The
total available dust mass is about 0.71 M⊙ in either nucleosynthesis model. The maximum massof silicate dust of 0.51 or 0.40 M⊙, depending on
the models, is smaller than the 2.4 M⊙ required to
fit the observed far-infrared/submm flux withpure silicate emission. The same holds for carbon
and iron dust. It is clear that any attempt to fit theobserved spectrum with a single dust species requires a larger mass of that particular dust species
than is available in the ejecta.
The far-infrared/submm fluxes could, however, be the sum of the emission from several different dust species in the ejecta. Figure 2, C and
Table 3. Model prediction of the mass of representative refractory elements synthesized in the
SN 1987A ejecta. Isotopes that contribute a large
fraction of the total atomic mass were accountedfor. Model 1, Theoretical calculations of elemental
abundance from (3). Model 2, Calculations from an
updated version of (35).
Elements
C
O
Mg
Si
Fe

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Mass (M⊙)
Model 1Model 2

0.114
1.48
0.183
0.101
0.083

0.26
0.24
0.04
0.14
0.075

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RESEARCH ARTICLESTable 4. The dust mass assumes 100% dust condensation of the available elemental mass (md). The
range of dust masses reflects the difference in compositions in Table 3. All silicates are assumed to be in
the form of MgO and SiO2 dust. The mass of carbon dust assumes that no substantial fraction of carbon islocked up in CO molecules.
md (M⊙)

Dust species

Model 1Model 2

Amorphous carbon
Silicate
Iron
Total

0.11
0.52
0.08
0.71

0.26
0.37
0.08
0.71

D, shows the predicted far-infrared SEDs arisingfrom dust in the ejecta of SN 1987A using ejecta
abundances from models 1 and 2, respectively(Table 4). Figure 2, C and D, suggests that asubstantial fraction of the major refractory elements are depleted onto dust and that the total
dust mass is about 0.4 to 0.7 M⊙.
Support for the presence of large amounts ofdust in the ejecta may come from Hubble Space
Telescope (HST) observations of the ejecta Ha
profile in 2004 and 2010 (36), which show the
redward part of the profile to be largely missing,which could be interpreted as implying thatemission from material at the far side of the ejecta suffers more extinction by intervening dust
than material at the near side.
The derived dust mass is about 103 times aslarge as and about 20 times as cold as that measured at mid-infrared wavelengths around 600 days
after the explosion was observed, soon after it
first condensed out of the ejecta (15, 16). Farinfrared and submm observatories with Herschel’ssensitivity did not exist at that time. It is possiblethat this submm dust mass existed at day 600.
However, it is also possible that this dust mass
grew by accretion over the past 20 years or that
initially optical/infrared-thick dust-bearing clumps
may have become optically thin at far-infraredand submm wavelengths. Overall, the observations
provide evidence for the efficient formation andgrowth of massive quantities of dust in SN ejecta.
Our result could affect the understanding of
the evolution of dust in galaxies. In the LMC, therate of type II supernovae is estimated to be one
per 300 years (37). If all type II supernovae form
typically 0.4 M⊙ of dust, the overall SN dust
injection rate into the ISM would be more than
10−3 M⊙ year–1. This is about 10 times as high as
the overall dust inputs measured from asymptotic
giant branch stars in the LMC (38, 39). With sucha high efficiency and with a dust lifetime of 2 ×
108 to 4 × 108 years (40), it would be possible toexplain a substantial fraction of the dust in the
LMC (about 1 × 106 M⊙) (41, 31) by a stellar
origin.
The large amount of dust inferred to be present
in the ejecta of SN 1987A is consistent withthat required to explain the dust masses in highredshift galaxies (42, 43), that is, 0.1 to 1.0 M⊙
of dust per SN, if the dust is not substantiallydestroyed during its injection into the ISM andsubsequent encounters with interstellar shocks.

Supernovae may therefore be important contributors of dust detected in such galaxies.
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minimum dust masses. We used three different dust
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and pure iron, whose refractive indices we took from
(49–51) and dust densities from (52–54). We calculated
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Mie theory. In the far-infrared/submm wavelength regime,
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the value of k is a maximum in the Herschel wavelength
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Acknowledgments: Herschel is a European Space Agency(ESA) space observatory with science instruments
provided by European-led principal investigatorconsortia and with important participation from NASA.
We acknowledge financial support from the NASA
Herschel Science Center, JPL contracts 1381522 and
1381650. We acknowledge the contributions and supportof the ESA, the PACS and SPIRE teams, the Herschel
Science Centre, the NASA Herschel Science Center, and
the PACS and SPIRE instrument control centers, without
which none of this work would have been possible.
We also thank the HERITAGE team for various inputs on
the data reduction. M.M. appreciates many discussions
and inputs from H. Hirashita, I. Sakon, R. Wesson,
K. Nomoto, and B. M. Swinyard. M.M. acknowledges
the award of a University College London Institute ofOrigins Fellowship, and M.L. acknowledges a European
Southern Observatory-Keele studentship.

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RESEARCH ARTICLES

23 March 2011; accepted 21 June 2011
Published online 7 July 2011;10.1126/science.1205983

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